What was the change in the Net cash provided by operating activities from 2018 to 2019?
{"": {"2019": "", "2018": "(in thousands)", "2017": ""}, "Net cash provided by operating activities": {"2019": 66235, "2018": 46412, "2017": 32514}, "Net cash used in investing activities": {"2019": -121324, "2018": -35019, "2017": -84615}, "Net cash provided by (used in) financing activities": {"2019": 116985, "2018": 13156, "2017": -332}}
net_cash_2019 = df["Net cash provided by operating activities"]["2019"]
net_cash_2018 = df["Net cash provided by operating activities"]["2018"]
answer = net_cash_2019 - net_cash_2018