What is the change in the projected benefit obligation from 2018 to 2019?
{"Projected benefit obligation": {"2019": 21190, "2018": 19510}, "Accumulated benefit obligation": {"2019": 21134, "2018": 19461}, "Fair value of plan assets": {"2019": 19388, "2018": 17757}}
projected_benefit_obligation_2019 = df["Projected benefit obligation"]["2019"]
projected_benefit_obligation_2018 = df["Projected benefit obligation"]["2018"]
answer = projected_benefit_obligation_2019 - projected_benefit_obligation_2018