Can somebody explain how they got this answer?

VEL Review M Howard Inc. has a defined benefit pension plan. On December 31 (the end of the fiscal year), the company received the PBO report from the actuary. The following information was included in the report: ending PBO $110,000, benefits paid to retirees, $10,000; interest cost, $7,200. The discount rate applied by the actuary was 8%. What was the beginning PBO? $90,000 O B $100,000 O C $107,200 O D $112,000