Table:
| Years Ended | July 27, 2019 | July 28, 2018 | July 29, 2017 |
| --- | --- | --- | --- |
| Cost of sales—product | $90 | $94 | $85 |
| Cost of sales—service | 130 | 133 | 134 |
| Share-based compensation expense in cost of sales . | 220 | 227 | 219 |
| Research and development . | 540 | 538 | 529 |
| Sales and marketing | 519 | 555 | 542 |
| General and administrative | 250 | 246 | 236 |
| Restructuring and other charges | 62 | 33 | 3 |
| Share-based compensation expense in operating expenses | 1,371 | 1,372 | 1,310 |
| Total share-based compensation expense | $1,591 | $1,599 | $1,529 |
| Income tax benefit for share-based compensation . | $542 | $558 | $451 |
Paragraphs:
(c) Summary of Share-Based Compensation Expense
Share-based compensation expense consists primarily of expenses for stock options, stock purchase rights, restricted stock, and RSUs granted to employees. The following table summarizes share-based compensation expense (in millions):
As of July 27, 2019, the total compensation cost related to unvested share-based awards not yet recognized was $3.3 billion, which is expected to be recognized over approximately 2.8 years on a weighted-average basis.
Question:
What was the change in the product cost of sales between 2017 and 2018?
Answer: 94-85 = 9