Management’s Discussion and Analysis of Financial Condition and Results of Operations – (continued) (Amounts in Millions, Except Per Share Amounts) LIQUIDITY AND CAPITAL RESOURCES CASH FLOW OVERVIEW The following tables summarize key financial data relating to our liquidity, capital resources and uses of capital.
## Table 0 ##
1 Reflects net income adjusted primarily for depreciation and amortization of fixed assets and intangible assets, amortization of restricted stock and other non-cash compensation, net losses on sales of businesses and deferred income taxes.2 Reflects changes in accounts receivable, accounts receivable billable to clients, other current assets, accounts payable and accrued liabilities.
Operating Activities Due to the seasonality of our business, we typically use cash from working capital in the first nine months of a year, with the largest impact in the first quarter, and generate cash from working capital in the fourth quarter, driven by the seasonally strong media spending by our clients.
Quarterly and annual working capital results are impacted by the fluctuating annual media spending budgets of our clients as well as their changing media spending patterns throughout each year across various countries.
The timing of media buying on behalf of our clients across various countries affects our working capital and operating cash flow and can be volatile.
In most of our businesses, our agencies enter into commitments to pay production and media costs on behalf of clients.
To the extent possible, we pay production and media charges after we have received funds from our clients.
The amounts involved, which substantially exceed our revenues, primarily affect the level of accounts receivable, accounts payable, accrued liabilities and contract liabilities.
Our assets include both cash received and accounts receivable from clients for these pass-through arrangements, while our liabilities include amounts owed on behalf of clients to media and production suppliers.
Our accrued liabilities are also affected by the timing of certain other payments.
For example, while annual cash incentive awards are accrued throughout the year, they are generally paid during the first quarter of the subsequent year.
Net cash provided by operating activities during 2018 was $565.1, which was a decrease of $316.7 as compared to 2017, primarily as a result of an increase in working capital usage of $436.4.
Working capital in 2018 was impacted by the spending levels of our clients as compared to 2017.
The working capital usage in both periods was primarily attributable to our media businesses.
Net cash provided by operating activities during 2017 was $881.8, which was an increase of $369.0 as compared to 2016, primarily as a result of an improvement in working capital usage of $415.6.
Working capital in 2017 benefited from the spending patterns of our clients compared to 2016.
Investing Activities Net cash used in investing activities during 2018 consisted of payments for acquisitions of $2,309.8, related mostly to the Acxiom Acquisition, and payments for capital expenditures of $177.1, related mostly to leasehold improvements and computer hardware and software.
Our cash flows were as follows for the years presented below:
## Table 1 ##
Operating Activities Net cash provided by operating activities of $29.1 million for the year ended December 31, 2007 consisted of net income of $10.3 million, adjusted for non-cash charges, primarily consisting of depreciation and amortization of $7.2 million, stock-based compensation expense of $5.6 million and deferred taxes of $4.7 million and a decrease in working capital of $0.9 million.
Net cash provided by operating activities of $17.1 million for the year ended December 31, 2006 consisted of net income of $5.4 million, adjusted for non-cash charges, primarily consisting of depreciation and amortization of $6.7 million, stock-based compensation expense of $6.4 million, deferred taxes of $0.9 million and a provision for bad debts of $0.7 million.
These non-cash charges were offset by an increase in cash used for working capital of $3.0 million.
Net cash provided by operating activities of $16.9 million for the year ended December 31, 2005 consisted of net income of $8.1 million, adjusted for non-cash charges, primarily consisting of depreciation and amortization of $5.6 million, stock-based compensation expense of $2.5 million and deferred taxes of $3.0 million.
These non-cash charges were offset by an increase in cash used for working capital of $2.7 million.
Investing Activities Net cash used in investing activities of $11.2 million for the year ended December 31, 2007 primarily consisted of the acquisition of TWS for $3.1 million, net purchases of securities-available-for-sale of $2.5 million, purchases of furniture, equipment and leasehold improvements of $1.5 million and capitalization of software development costs of $3.4 million.
Net cash provided by investing activities of $4.2 million for the year ended December 31, 2006 consisted of net proceeds of securities-available-for-sale of $11.0 million, offset by purchases of furniture, equipment and leasehold improvements of $2.7 million and capitalization of software development costs of $4.1 million.
Net cash used in investing activities of $59.0 million for the year ended December 31, 2005 consisted of net purchases of securities-available-for-sale of $60.0 million, purchases of furniture, equipment and leasehold improvements of $1.4 million and capitalization of software development costs of $3.4 million, offset by maturity of short-term investments of $5.8 million.
Financing Activities Net cash used in financing activities of $27.0 million for the year ended December 31, 2007 primarily consisted of $34.6 million for the purchase of treasury stock, offset by proceeds from the exercise of stock options of $5.2 million and excess tax benefits from stock-based compensation of $2.2 million.
Net cash provided by financing activities of $2.8 million for the year ended December 31, 2006 consisted of proceeds from the exercise of stock options of $3.8 million and excess tax benefits from stock-based compensation of $1.7 million, offset by the purchase of treasury stock of $2.7 million.
Net cash provided by financing activities of $2.7 million for the year ended December 31, 2005 consisted of proceeds from the exercise of stock options of $2.7 million.
MARKETAXESS HOLDINGS INC.  NOTES TO CONSOLIDATED FINANCIAL STATEMENTS — (Continued) The fair value of each option award is estimated on the date of grant using the Black-Scholes closed-form model.
The Company believes that the use of the Black-Scholes model meets the fair value measurement objectives of SFAS 123R and reflects all substantive characteristics of the instruments being valued.
The determination of fair value of share-based payment awards on the date of grant using an option-pricing model is affected by the Company’s stock price as well as assumptions regarding a number of highly complex and subjective variables, including the expected stock price volatility over the term of the awards, the risk-free interest rate and the expected term.
Expected volatilities are based on historical volatility of the Company’s stock and a peer group.
The risk-free interest rate is based on U. S.  Treasury securities with a maturity value approximating the expected term of the option.
The expected term represents the period of time that options granted are expected to be outstanding based on actual and projected employee stock option exercise behavior and was increased from four years to five years in May 2006.
The following table represents the assumptions used for the Black-Scholes option-pricing model to determine the per share weighted-average fair value for options granted for the years ended December 31, 2007, 2006 and 2005:
## Table 2 ##
The following table reports stock option activity during the three years ended December 31, 2007 and the intrinsic value as of December 31, 2007:
## Table 3 ##
The intrinsic value is the amount by which the closing price of the Company’s common stock on December 31, 2007 of $12.83 or the price on the day of exercise exceeds the exercise price of the stock options multiplied by the number of shares.
As of December 31, 2007, there was $6.6 million of total unrecognized compensation cost related to non-vested stock options.
That cost is expected to be recognized over a weighted-average period of 1.6 years.

<table><tr><td></td><td>Years ended December 31,</td></tr><tr><td>Cash Flow Data</td><td>2018</td><td>2017</td><td>2016</td></tr><tr><td>Net income, adjusted to reconcile to net cash provided by operating activities<sup>1</sup></td><td>$1,013.0</td><td>$852.1</td><td>$1,018.6</td></tr><tr><td>Net cash (used in) provided by working capital<sup>2</sup></td><td>-431.1</td><td>5.3</td><td>-410.3</td></tr><tr><td>Changes in other non-current assets and liabilities</td><td>-16.8</td><td>24.4</td><td>-95.5</td></tr><tr><td>Net cash provided by operating activities</td><td>$565.1</td><td>$881.8</td><td>$512.8</td></tr><tr><td>Net cash used in investing activities</td><td>-2,491.5</td><td>-196.2</td><td>-263.9</td></tr><tr><td>Net cash provided by (used in) financing activities</td><td>1,853.2</td><td>-1,004.9</td><td>-666.4</td></tr></table>
<table><tr><td></td><td colspan="3">Year Ended December 31,</td></tr><tr><td></td><td>2007</td><td>2006</td><td>2005</td></tr><tr><td></td><td colspan="3">(In thousands)</td></tr><tr><td>Net cash provided by operating activities</td><td>$29,120</td><td>$17,101</td><td>$16,908</td></tr><tr><td>Net cash (used in) provided by investing activities</td><td>-11,179</td><td>4,231</td><td>-59,034</td></tr><tr><td>Net cash (used in) provided by financing activities</td><td>-27,015</td><td>2,818</td><td>2,709</td></tr><tr><td>Effect of exchange rate changes on cash</td><td>-215</td><td>-339</td><td>-46</td></tr><tr><td>Net (decrease) increase for the period</td><td>$-9,289</td><td>$23,811</td><td>$-39,463</td></tr></table>
<table><tr><td></td><td>2007</td><td>2006</td><td> 2005</td></tr><tr><td>Weighted-Average Expected Life (years)</td><td>5.0</td><td>4.6</td><td>3.0</td></tr><tr><td>Weighted-Average Risk-Free Interest Rate</td><td>4.7%</td><td>4.7%</td><td>3.6%</td></tr><tr><td>Weighted-Average Expected Volatility</td><td>44.6%</td><td>41.8%</td><td>20.7%</td></tr><tr><td>Weighted-Average Fair Value per Option Granted</td><td>$6.02</td><td>$4.45</td><td>$2.71</td></tr></table>
<table><tr><td></td><td></td><td></td><td> Remaining </td><td></td></tr><tr><td></td><td>Number of</td><td> Weighted-Average </td><td> Contractual </td><td></td></tr><tr><td></td><td>Shares</td><td> Exercise Price</td><td> Term</td><td> Intrinsic Value  (In thousands)</td></tr><tr><td>Outstanding at December 31, 2004</td><td>4,907,582</td><td>$5.17</td><td></td><td></td></tr><tr><td>Granted</td><td>1,400,750</td><td>$13.70</td><td></td><td></td></tr><tr><td>Canceled</td><td>-211,902</td><td>$13.04</td><td></td><td></td></tr><tr><td>Exercised</td><td>-927,623</td><td>$2.92</td><td></td><td></td></tr><tr><td>Outstanding at December 31, 2005</td><td>5,168,807</td><td>$7.56</td><td></td><td></td></tr><tr><td>Granted</td><td>2,297,150</td><td>$10.87</td><td></td><td></td></tr><tr><td>Canceled</td><td>-983,981</td><td>$10.98</td><td></td><td></td></tr><tr><td>Exercised</td><td>-768,116</td><td>$4.94</td><td></td><td></td></tr><tr><td>Outstanding at December 31, 2006</td><td>5,713,860</td><td>$8.65</td><td></td><td></td></tr><tr><td>Granted</td><td>638,500</td><td>$13.26</td><td></td><td></td></tr><tr><td>Canceled</td><td>-550,947</td><td>$11.55</td><td></td><td></td></tr><tr><td>Exercised</td><td>-774,521</td><td>$7.76</td><td></td><td>$5,736</td></tr><tr><td>Outstanding at December 31, 2007</td><td>5,026,892</td><td>$9.05</td><td>6.9</td><td>$21,064</td></tr><tr><td>Exercisable at December 31, 2007</td><td>3,470,657</td><td>$7.88</td><td>6.0</td><td>$18,967</td></tr></table>

Question: What is the sum of the Weighted-Average Expected Life (years) in the years where Weighted-Average Fair Value per Option Granted is positive?