What was the change in Fair value of plan assets from 2018 to 2019?
{"Projected benefit obligation": {"2019": 60437, "2018": 51499}, "Accumulated benefit obligation": {"2019": 55941, "2018": 47713}, "Fair value of plan assets": {"2019": 12997, "2018": 12486}}
fair_value_of_plan_assets_2019 = df["Fair value of plan assets"]["2019"]
fair_value_of_plan_assets_2018 = df["Fair value of plan assets"]["2018"]
answer = fair_value_of_plan_assets_2019 - fair_value_of_plan_assets_2018