What was the change in the Sales and marketing between 2018 and 2019?
{"Sales and marketing": {"2019": 2075, "2018": 1196, "2017": 561}, "General and administrative": {"2019": 6474, "2018": 4901, "2017": 2638}, "Research and development": {"2019": 12054, "2018": 7332, "2017": 4214}, "Total stock-based compensation expense": {"2019": 20603, "2018": 13429, "2017": 7413}}
sales_and_marketing_2019 = df["Sales and marketing"]["2019"]
sales_and_marketing_2018 = df["Sales and marketing"]["2018"]
answer = sales_and_marketing_2019 - sales_and_marketing_2018