Here is the homework question:

A partially completed pension spreadsheet showing the relationships among the elements that constitute Carney, Inc.s defined benefit pension plan follows. Six years earlier, Carney revised its pension formula and recalculated benefits earned by employees in prior years using the more generous formula. The prior service cost created by the recalculation is being amortized at the rate of $6 million per year. At the end of 2016, the pension formula was amended again, creating an additional prior service cost of $40 million. The expected rate of return on assets and the actuarys discount rate were 10%, and the average remaining service life of the active employee group is 10 years.

I found the solution in the solutions manual for a prior year for the same question, just with different numbers.I can use that to help guide me, but what I don't undersatnd is how you come up with the service cost?