Table:
|  | Years ended December 31, |  |  | 2019 vs 2018 | 2018 vs 2017 |
| --- | --- | --- | --- | --- | --- |
|  | 2019 | 2018 | 2017 | % Change | % Change |
|  | (in thousands, except percentages) |  |  |  |  |
| Sales and marketing | $ 472,841 | $ 350,069 | $ 225,694 | 35.1 % | 55.1 % |
| Percentage of total revenues | 30.0 % | 32.6 % | 33.5 % |  |  |
Paragraphs:
Operating Expense
Sales and Marketing
Sales and marketing expenses increased $122.8 million, or 35.1%, for the year ended December 31, 2019 compared to the same period in 2018, due to an increase of $70.4 million in expenditures on marketing programs to support the growth of our business, such as advertisements on search engines and social media, brand campaigns, event sponsorships and payments to partners. Employee-related costs increased $48.7 million ($14.1 million of which related to stock-based compensation and related payroll taxes) to support the growth of the business including in Shopify Plus and International operations. Computer hardware and software costs increased by $3.7 million, largely due to the growth in sales and marketing headcount
Sales and marketing expenses increased $124.4 million, or 55.1%, for the year ended December 31, 2018 compared to the same period in 2017, primarily due to an increase of $80.7 million in employee-related costs. In addition to employee-related costs, marketing costs increased by $39.7 million and computer hardware and software costs increased by $4.0 million.
Question:
What is the average sales and marketing expenses for 2018 and 2019?