What was the percentage change in Interest expense in 2019 from 2018?
{"Average daily utilization": {"2019": 87800.0, "2018": 106189.0, "2017": 268775.0}, "Interest expense (1)": {"2019": 3465.0, "2018": 3817.0, "2017": 6668.0}, "Weighted average interest rate (1)": {"2019": 3.9, "2018": 3.6, "2017": 2.5}}
interest_expense_2019 = df["Interest expense (1)"]["2019"]
interest_expense_2018 = df["Interest expense (1)"]["2018"]
answer = ( interest_expense_2019 - interest_expense_2018 ) / interest_expense_2018 * 100.0