The service cost for 2021 is -$475,200.
The actual experience was better than what was expected, and the plan did not need to accrue as much expense.
How to solve
Calculate the expected return on assets for 2021
expected_return_on_assets_2021 = 5,760,000 * 0.1 = $576,000
Calculate the service cost for 2021
service_cost_2021 = (-6,504,000 - (-6,000,000)) - (576,000 - 5,760,000) - (624,000 - 696,000)
= -475,200
Since the service cost is a negative number, it means that the plan experienced a favorable deviation in 2021.
The service cost for 2021 is -$475,200. Since the service cost is a negative number, it means that the plan experienced a favorable deviation in 2021.
This means that the actual experience was better than what was expected, and the plan did not need to accrue as much expense.