Sheffield Co. purchased equipment for $418,800 which was estimated to have a useful life of 10 years with a salvage value of $10,000 at the end of that time. Depreciation has been entered for 7 years on a straight-line basis. In 2021, it is determined that the total estimated life should be 15 years with a salvage value of $5,200 at the end of that time. (a) Prepare the entry (if amy) to correct the prior years' depreciation. (b) Prepare the entry to record depreciation for 2021. (Credit account titles are automatically indented when amount is entered. Do not indent manually. If no entry is required, select "No Entry" for the account titles and enter O for the amounts)