What was the percentage change in Interest cost between 2018 and 2019?
{"Service cost": {"2019": 272, "2018": 841, "2017": "$  \u2014"}, "Interest cost": {"2019": 1211, "2018": 802, "2017": 809}, "Expected return on plan assets": {"2019": -615, "2018": -665, "2017": -597}, "Amortization of actuarial gains and losses": {"2019": 411, "2018": 478, "2017": 503}, "Net periodic pension cost": {"2019": 1279, "2018": 1456, "2017": 715}}
interest_cost_2019 = df["Interest cost"]["2019"]
interest_cost_2018 = df["Interest cost"]["2018"]
answer = ( interest_cost_2019 - interest_cost_2018 ) / interest_cost_2018 * 100.0