The following incomplete (columns have missing amounts) pension spreadsheet is for old tucson corporation (otc). plan prior service net pension net pension ($ in millions) debit (credit) pbo assets cost (gain)loss expense cash (liability)/asset beginning balance (500 ) 58 service cost 62 interest cost expected return on assets (23 ) gain/loss on assets (2 ) amortization of: prior service cost (6 ) net gain/loss loss on pbo (25 ) 25 contributions to fund (56 ) retiree benefits paid 43 (43 ) ending balance (574 ) 288 54 78 (286 ) what was the prior service cost at the beginning of the year?