What was the percentage change in unearned revenue between 2018 and 2019?
{"Accounts receivable": {"December 31, 2019": 90531, "December 31, 2018": 99385}, "Contract assets (1)": {"December 31, 2019": 2812, "December 31, 2018": 3766}, "Unearned revenue": {"December 31, 2019": 11963, "December 31, 2018": 17940}, "Non-current unearned revenue": {"December 31, 2019": 6012, "December 31, 2018": 5296}}
unearned_revenue_2019 = df["Unearned revenue"]["December 31, 2019"]
unearned_revenue_2018 = df["Unearned revenue"]["December 31, 2018"]
answer = (unearned_revenue_2019 - unearned_revenue_2018) / unearned_revenue_2018 * 100.0