What is the percentage increase in working capital from 2017 to 2019?
{"": {"2019": "", "2018": "(in thousands)", "2017": ""}, "Cash and cash equivalents": {"2019": 36617, "2018": 60444, "2017": 67495}, "Marketable securities": {"2019": 434761, "2018": 339424, "2017": 297115}, "Working capital": {"2019": 368912, "2018": 370445, "2017": 361621}, "Net cash provided by operating activities": {"2019": 72819, "2018": 83085, "2017": 61893}, "Net cash used in investing activities": {"2019": -103579, "2018": -56237, "2017": -207907}, "Net cash provided by (used in) financing activities": {"2019": 6933, "2018": -33899, "2017": 5477}}
working_capital_2019 = df["Working capital"]["2019"]
working_capital_2017 = df["Working capital"]["2017"]
answer = ( working_capital_2019 - working_capital_2017 ) / working_capital_2017 * 100.0