What is the percentage change in net interest expense of long-term debt from 2018 to 2019?
{"Long-term debt": {"2019": 385.9, "2018": 161.2, "2017": 203.6}, "Short-term debt": {"2019": 15.0, "2018": 4.8, "2017": 0.6}, "Interest income": {"2019": -6.8, "2018": -3.8, "2017": -3.7}, "Interest capitalized": {"2019": -2.7, "2018": -3.5, "2017": -5.0}, "": {"2019": 391.4, "2018": 158.7, "2017": 195.5}}
longterm_debt_2019 = df["Long-term debt"]["2019"]
longterm_debt_2018 = df["Long-term debt"]["2018"]
answer = ( longterm_debt_2019 - longterm_debt_2018 ) / longterm_debt_2018 * 100.0