What was the increase / (decrease) in the Average term: long-term debt (in years) from 2018 to 2019?
{"Average cost of indebtedness(2)": {"2020 Guidelines(1)": 4.4, "2019": 4.4, "2018": 4.4}, "Fixed rate indebtedness(3)": {"2020 Guidelines(1)": 78.0, "2019": 78.0, "2018": 72.0}, "Average term: long-term debt (in years)": {"2020 Guidelines(1)": 3.9, "2019": 4.9, "2018": 5.7}, "Net indebtedness(4) / adjusted EBITDA(5)": {"2020 Guidelines(1)": 2.3, "2019": 2.6, "2018": 3.8}, "Adjusted EBITDA / financial expense(5)": {"2020 Guidelines(1)": -6.0, "2019": 6.3, "2018": 5.4}}
average_term_longterm_debt_in_years_2019 = df["Average term: long-term debt (in years)"]["2019"]
average_term_longterm_debt_in_years_2018 = df["Average term: long-term debt (in years)"]["2018"]
answer = average_term_longterm_debt_in_years_2019 - average_term_longterm_debt_in_years_2018