Table:
|  |  | Year Ended December 31, |  |
| --- | --- | --- | --- |
|  | 2019 | 2018 | 2017 |
| Cost of revenue | $10.6 | $7.0 | $6.0 |
| Research and development | 17.0 | 14.3 | 12.5 |
| Selling and marketing | 14.8 | 14.1 | 11.7 |
| General and administrative | 37.0 | 42.9 | 39.6 |
| Share-based compensation expense | 79.4 | 78.3 | 69.8 |
| Related income tax benefits at federal rate (1) | (16.7) | (16.4) | (24.4) |
| Share-based compensation expense, net of taxes | $62.7 | $61.9 | $45.4 |
Paragraphs:
Note 11: Share-Based Compensation
Total share-based compensation expense related to the Company's stock options, RSUs, stock grant awards and ESPP were recorded within the Consolidated Statements of Operations and Comprehensive Income as follows (in millions):
(1) Recognition of related income tax benefits are the result of the adoption of ASU 2016-09 during the first quarter of 2017 through a cumulative effect adjustment of $68.1 million recorded as a credit to retained earnings as of January 1, 2017. Tax benefit is calculated using the federal statutory rate of 21% during the years ended December 31, 2019 and December 31, 2018, and 35% for the year ended December 31, 2017.
At December 31, 2019, total unrecognized share-based compensation expense, net of estimated forfeitures, related to non-vested RSUs with service, performance and market conditions was $74.9 million, which is expected to be recognized over a weighted-average period of 1.3 years. The total intrinsic value of stock options exercised during the year ended December 31, 2019 was $3.9 million.
The Company received cash of $1.7 million and $26.2 million from the exercise of stock options and the issuance of shares under the ESPP, respectively. Upon option exercise, vesting of RSUs, stock grant awards, or completion of a purchase under the ESPP, the Company issues new shares of common stock.
Question:
What is the average Cost of revenue for December 31, 2018 and 2019?
Answer: (10.6+7.0) / 2 = 8.8