the following refers to the pension spreadsheet (columns have missing amounts) for the current year for pancho villa enterprises (pve). ($ in millions) debit(credit) pbo plan assets prior service cost net (gain)/loss pension expense cash net pension (liability)/ asset beginning balance 464 74 69 65 service cost (99 ) interest cost (39 ) expected return on assets 69 gain/loss on assets 5 amortization of: prior service cost net gain/loss (3 ) loss on pbo (79 ) contributions to fund 54 retiree benefits paid ending balance (544 ) 65 136 what was the pbo at the beginning of the year?