What is the percentage change for cash and cash equivalents between 2018 and 2019?
{"": {"2019": "", "2018": "", "2017": "(In thousands)", "2016": "", "2015": ""}, "Cash and cash equivalents": {"2019": 19505, "2018": 18017, "2017": 22553, "2016": 26838, "2015": 35128}, "Working capital": {"2019": 1116, "2018": 6356, "2017": 7646, "2016": 14643, "2015": 16046}, "Total assets": {"2019": 54538, "2018": 43424, "2017": 45672, "2016": 53530, "2015": 68579}, "Stockholders' equity": {"2019": 10863, "2018": 14059, "2017": 13078, "2016": 18064, "2015": 21387}}
cash_2019 = df["Cash and cash equivalents"]["2019"]
cash_2018 = df["Cash and cash equivalents"]["2018"]
answer = (cash_2019 - cash_2018) / cash_2018 * 100.0