Discussion of Cash Flows
During 2019, the $4.8 million of net cash provided by operating activities consisted of our net income of $5.3 million, and included non-cash charges for depreciation and amortization of $2.5 million, and stock-based compensation of $1.5 million, offset by a tax benefit from a partial release of the valuation allowances of $3.3 million and a net cash outflow of $1.8 million from changes in working capital. The changes in working capital were principally driven by an increase in accounts receivable of $2.2 million, an increase in inventory of $0.7 million, an increase in contract assets of $0.4 million, and an increase in other assets of $0.2 million, all partially offset by decreases in accounts payable and accrued expenses of $0.6 million and contract liabilities of $1.2 million,
In 2018, the $3.3 million of net cash used in operating activities consisted of our net income of $11.0 million and included a gain recognized on the sale of our optoelectronic segment that was sold in July 2018 of $8.6 million in addition to non-cash charges for depreciation and amortization of $1.2 million and stock-based compensation of $0.6 million, offset by a net cash outflow of $7.6 million from changes in working capital. The changes in working capital were principally driven by an increase in inventory of $1.0 million, and increase in accounts receivable of $6.2 million, and increase in contract assets of $0.8 million, and an increase in accounts payable and accrued liabilities of $0.5 million, all partially offset by a $1.8 million decrease in other assets.
Cash used in investing activities in 2019 consisted primarily of the $19.0 million payment for our acquisition of GP, $0.5 million of fixed asset additions and $0.3 million of capitalized intellectual property costs.
Cash provided by investing activities in 2018 consisted primarily of the proceeds from the sale of our optoelectronic segment of $15.8 million, partially offset by the $5.0 million payment for our acquisition of MOI, $0.4 million of fixed asset additions and $0.4 million of capitalized intellectual property rights.
Cash used in financing activities for the year ended December 31, 2019 was $2.4 million, compared to $1.2 million in 2018. During 2019, we repaid $0.6 million on our term loans with SVB and used $2.2 million to repurchase our common stock under our stock repurchase program. These payments were partially offset by $0.4 million received from exercises of stock options and warrants. During 2018, we repaid $1.8 million on our outstanding term loan with SVB and used $0.5 million to repurchase our common stock under our stock repurchase program. These payments were partially offset by $1.1 million received from exercises of stock options and warrants.
Table:
 | Years ended December 31, | 
 | 2019 | 2018
Net cash provided by/(used in) operating activities | $4,798,201 | $(3,308,826)
Net cash (used in)/provided by investing activities | (19,814,991) | 10,037,123
Net cash used in financing activities | (2,437,560) | (1,249,564)
Net (decrease)/increase in cash and cash equivalents | $(17,454,350) | $5,478,733


Question: In which year was Net cash provided by/(used in) operating activities negative?
Answer: 2018
Calculation: locate and analyze Net cash provided by/(used in) operating activities in row 3