I can not figure out how to calculate optional accumulated depreciation for this problem. I know that the journal entries are Debit Accumulated Depreciation and Credit Buildings and Equipment. I just need to know the formula to calculate the depreciation.

Pop Corporation acquired 70 percent of Soda Company's voting common shares on January 1, 20X2, for $112,700. At that date, the noncontrolling interest had a fair value of $48,300 and Soda reported $71,000 of common stock outstanding and retained earnings of $31,000. The differential is assigned to buildings and equipment, which had a fair value $28,000higher than book value and a remaining 10-year life, and to patents, which had a fair value $31,000 higher than book value and a remaining life of five years at the date of the business combination. Trial balances for the companies as of December 31, 20X3, are as follows:

Pop CorporationSoda CompanyItemDebitCreditDebitCreditCash & Accounts Receivable$16,400$22,600Inventory166,00036,000Land81,00041,000Buildings & Equipment350,000261,000Investment in Soda Company117,200Cost of Goods Sold187,00080,800Depreciation Expense20,00015,000Interest Expense17,0006,200Dividends Declared31,00016,000Accumulated Depreciation$141,000$85,000Accounts Payable93,40036,000Bonds Payable219,25094,000Bond Premium1,600Common Stock121,00071,000Retained Earnings128,90061,000Sales261,000130,000Other Income10,600Income from Soda Company10,450$985,600$985,600$478,600$478,600

On December 31, 20X2, Soda purchased inventory for $31,500 and sold it to Pop for $45,000. Pop resold $30,000 of the inventory (i.e., $30,000 of the $45,000 acquired from Soda)during 20X3 and had the remaining balance in inventory at December 31, 20X3.

During 20X3, Soda sold inventory purchased for $56,000 to Pop for $80,000, and Pop resold all but $25,000 of its purchase. On March 10, 20X3, Pop sold inventory purchased for $15,000 to Soda for $30,000. Soda sold all but $7,800 of the inventory prior to December 31, 20X3. Assume Pop uses the fully adjusted equity method, that both companies use straight-line depreciation, and that no property, plant, and equipment has been purchased since the acquisition.

Please help calculate optional accumulated depreciation.