The following table provides the weighted average assumptions used in the Black-Scholes option-pricing model for grants and the resulting weighted average grant date fair value per share of stock options granted for the years ended December 31:
## Table 0 ##
The Company used the actual historical experience of exercises or expirations of the 2009 grant to determine the expected stock option life.
The Company began granting stock options at the time of its initial public offering in April 2008.
Expected volatility is based on a weighted average of historic volatilities of traded common stock of peer companies (regulated water companies) over the expected term of the stock options and historic volatilities of the Company’s common stock during the period it has been publicly traded.
The dividend yield is based on the Company’s expected dividend payments and the stock price on the date of grant.
The riskfree interest rate is the market yield on U. S.  Treasury strips with maturities similar to the expected term of the stock options.
The exercise price of the stock options is equal to the fair market value of the underlying stock on the date of option grant.
Stock options vest over periods ranging from one to three years and have a maximum term of seven years from the effective date of the grant.
The following table provides stock option activity for the year ended December 31, 2018:
As of December 31, 2018, less than $1 million of total unrecognized compensation cost related to nonvested stock options is expected to be recognized over the remaining weighted average period of less than one year.
The total fair value of stock options vested was $1 million, $2 million and $1 million for the years ended December 31, 2018, 2017 and 2016, respectively.
The following table provides additional information regarding stock options exercised during the years ended December 31:
Stock Units During 2018, 2017 and 2016, the Company granted RSUs to certain employees under the 2007 Plan and 2017 Omnibus Plan, as applicable.
RSUs generally vest based on continued employment with the Company over periods ranging from one to three years.
NORTHROP GRUMMAN CORPORATION -27- Selected financial highlights are presented in the table below:
## Table 1 ##
Sales 2018 – Sales increased $4.1 billion, or 16 percent, as compared with 2017, due to the addition of $3.3 billion of sales from Innovation Systems and higher sales at Aerospace Systems and Mission Systems, partially offset by lower sales at Technology Services.2017 – Sales increased $1.3 billion, or 5 percent, as compared with 2016, primarily due to higher sales at Aerospace Systems and Mission Systems.
See “Segment Operating Results” below for further information by segment and “Product and Service Analysis” for product and service detail.
See Note 15 to the consolidated financial statements for information regarding the company’s sales by customer type, contract type and geographic region for each of our segments.
Operating Income and Margin Rate 2018 – Operating income increased $562 million, or 17 percent, as compared with 2017, primarily due to a $544 million increase in segment operating income, which includes the addition of $343 million of operating income from Innovation Systems, and a $42 million decrease in unallocated corporate expense, partially offset by a $25 million decrease in our net FAS (service)/CAS pension adjustment, all of which are further discussed in “Segment Operating Results.
” Lower operating costs and expenses as a percentage of sales increased our operating margin rate to 12.6 percent from 12.4 percent in the prior year period and was principally driven by a higher segment operating margin rate, as described in “Segment Operating Results,” and the previously noted decrease in unallocated corporate expense, partially offset by the decrease in our net FAS (service)/CAS pension adjustment.
G&A as a percentage of sales decreased to 10.0 percent in 2018 from 10.4 percent in 2017, principally due to higher sales volume.2017 – Operating income for 2017 decreased $59 million, or 2 percent, as compared with 2016, primarily due to a $280 million increase in unallocated corporate expense, partially offset by a $181 million increase in our net FAS (service)/CAS pension adjustment and a $39 million increase in segment operating income, all of which are further discussed in “Segment Operating Results.
” Higher operating costs and expenses as a percentage of sales reduced our operating margin rate to 12.4 percent from 13.3 percent in the prior year period and principally was driven by the previously noted increase in unallocated corporate expense and a lower segment operating margin rate, as described in “Segment Operating Results,” partially offset by the increase in our net FAS (service)/CAS pension adjustment.
G&A as a percentage of sales decreased to 10.4 percent in 2017 from 10.7 percent in 2016, principally due to higher sales volume.
For further information regarding product and service operating costs and expenses, see “Product and Service Analysis” below
NORTHROP GRUMMAN CORPORATION -33- MISSION SYSTEMS
## Table 2 ##
2018 – Mission Systems sales for 2018 increased $239 million, or 2 percent, as compared with 2017, primarily due to higher Sensors and Processing volume, partially offset by lower Cyber and ISR and Advanced Capabilities volume.
Sensors and Processing sales increased principally due to higher volume on restricted programs, communications programs, F-35 and electro-optical/infrared (EO/IR) self-protection programs.
Cyber and ISR sales decreased primarily due to ramp-down on a restricted ISR program.
Advanced Capabilities sales reflect lower volume on the Joint National Integration Center Research and Development (JRDC) program and follow on activity, partially offset by higher volume on several programs, including the Integrated Air and Missile Defense Battle Command System program.
Operating income for 2018 increased $78 million, or 5 percent, due to a higher operating margin rate and higher sales.
Operating margin rate increased to 13.0 percent from 12.6 percent primarily due to improved performance on Cyber and ISR and Sensors and Processing programs, partially offset by a $32 million benefit recognized in the prior year in connection with the 2017 Cost Claim described above.2017 – Mission Systems sales for 2017 increased $309 million, or 3 percent, as compared with 2016 primarily due to higher Sensors and Processing volume, partially offset by lower Cyber and ISR volume.
Sensors and Processing sales increased principally due to higher volume on F-35 sensors, EO/IR self-protection programs, communications programs and the SABR program.
These increases were partially offset by lower volume on international groundbased radar programs.
Cyber and ISR sales decreased primarily due to lower volume on restricted ISR programs.
Operating income for 2017 decreased $26 million, or 2 percent, primarily due to a lower operating margin rate, partially offset by higher sales and $32 million recognized in connection with the 2017 Cost Claim described above.
Operating margin rate decreased to 12.6 percent from 13.2 percent primarily due to lower margin rates on Sensors and Processing and Cyber and ISR programs principally resulting from lower performance and changes in contract mix.
This decrease was partially offset by improved margin rates at Advanced Capabilities primarily due to the prior year including a $49 million forward loss provision on an Advanced Capabilities program.
TECHNOLOGY SERVICES
## Table 3 ##
2018 – Technology Services sales for 2018 decreased $390 million, or 8 percent, as compared with 2017, due to lower volume on Advanced Defense Services and System Modernization and Services programs, partially offset by higher volume on Global Logistics and Modernization programs.
Advanced Defense Services and System Modernization and Services sales decreased primarily due to the completion of several programs, including JRDC, partially offset by higher volume on the Saudi Arabian Ministry of National Guard Training Support program (through our interest in a joint venture for which we consolidate the financial results).
Global Logistics and Modernization sales increased primarily due to higher volume for several programs, including the Special Electronic Mission Aircraft program, partially offset by lower volume from the completion of the KC-10 program.
Operating income for 2018 decreased $6 million, or 1 percent, primarily due to lower sales, partially offset by a higher operating margin rate.
Operating margin rate increased to 10.3 percent from 9.6 percent primarily due to the close-out of a state IT outsourcing program.2017 – Technology Services sales for 2017 decreased $78 million, or 2 percent, as compared with 2016, primarily due to lower volume on System Modernization and Services programs, partially offset by higher volume on Global Logistics and Modernization programs.
System Modernization and Services sales decreased principally due to the completion of several programs in 2016 and 2017.
Global Logistics and Modernization sales increased primarily due

<table><tr><td></td><td>2018</td><td>2017</td><td>2016</td></tr><tr><td>Intrinsic value</td><td>$9</td><td>$10</td><td>$18</td></tr><tr><td>Exercise proceeds</td><td>7</td><td>11</td><td>15</td></tr><tr><td>Income tax benefit realized</td><td>2</td><td>3</td><td>6</td></tr></table>
<table><tr><td></td><td colspan="3">Year Ended December 31</td><td colspan="2">% Change in</td></tr><tr><td>$ in millions, except per share amounts</td><td>2018</td><td>2017</td><td>2016</td><td>2018</td><td>2017</td></tr><tr><td>Sales</td><td>$30,095</td><td>$26,004</td><td>$24,706</td><td>16%</td><td>5%</td></tr><tr><td>Operating costs and expenses</td><td>26,315</td><td>22,786</td><td>21,429</td><td>15%</td><td>6%</td></tr><tr><td>Operating costs and expenses as a % of sales</td><td>87.4%</td><td>87.6%</td><td>86.7%</td><td></td><td></td></tr><tr><td>Operating income</td><td>3,780</td><td>3,218</td><td>3,277</td><td>17%</td><td>-2%</td></tr><tr><td>Operating margin rate</td><td>12.6%</td><td>12.4%</td><td>13.3%</td><td></td><td></td></tr><tr><td>Mark-to-market pension and OPB (expense) benefit</td><td>-655</td><td>536</td><td>-950</td><td>NM</td><td>NM</td></tr><tr><td>Federal and foreign income tax expense</td><td>513</td><td>1,360</td><td>638</td><td>-62%</td><td>113%</td></tr><tr><td>Effective income tax rate</td><td>13.7%</td><td>32.2%</td><td>23.8%</td><td></td><td></td></tr><tr><td>Net earnings</td><td>3,229</td><td>2,869</td><td>2,043</td><td>13%</td><td>40%</td></tr><tr><td>Diluted earnings per share</td><td>18.49</td><td>16.34</td><td>11.32</td><td>13%</td><td>44%</td></tr></table>
<table><tr><td></td><td colspan="3">Year Ended December 31</td><td colspan="2">% Change in</td></tr><tr><td>$ in millions</td><td>2018</td><td>2017</td><td>2016</td><td>2018</td><td>2017</td></tr><tr><td>Sales</td><td>$11,709</td><td>$11,470</td><td>$11,161</td><td>2%</td><td>3%</td></tr><tr><td>Operating income</td><td>1,520</td><td>1,442</td><td>1,468</td><td>5%</td><td>-2%</td></tr><tr><td>Operating margin rate</td><td>13.0%</td><td>12.6%</td><td>13.2%</td><td></td><td></td></tr></table>
<table><tr><td></td><td colspan="3">Year Ended December 31</td><td colspan="2">% Change in</td></tr><tr><td>$ in millions</td><td>2018</td><td>2017</td><td>2016</td><td>2018</td><td>2017</td></tr><tr><td>Sales</td><td>$4,297</td><td>$4,687</td><td>$4,765</td><td>-8%</td><td>-2%</td></tr><tr><td>Operating income</td><td>443</td><td>449</td><td>456</td><td>-1%</td><td>-2%</td></tr><tr><td>Operating margin rate</td><td>10.3%</td><td>9.6%</td><td>9.6%</td><td></td><td></td></tr></table>

Question: What's the average of the Operating costs and expenses for Year Ended December 31 in the years where Sales for Year Ended December 31 is positive? (in million)
Answer: 23510