Assume that at the beginning of the current year, a company has a net gain-AOCI of $25,000,000. At the same time, assume the PBO and the plan assets are $200,000,000 and $150,000,000, respectively. The average remaining service period for the employees expected to receive benefits is 10 years. What is the amount of amortization to pension expense for the year?

A) $500,000.

B) $2,500,000.

C) $1,500,000.

D) $3,000,000.

The answer is A) 500,000

Can you please explain in detail why and how you get this answer. I see the explanation of [25000000-(200000000*10%)/10], but still having difficulty to understand this.