What was the change in working capital between 2017 and 2018?
{"Cash and cash equivalents": {"2019": 119629, "2018": 146061, "2017": 96329}, "Accounts receivable, net": {"2019": 76373, "2018": 49510, "2017": 40634}, "Working capital": {"2019": 167879, "2018": 152793, "2017": 119433}}
working_capital_2018 = df["Working capital"]["2018"]
working_capital_2017 = df["Working capital"]["2017"]
answer = working_capital_2018 - working_capital_2017