Peter M. Dell Co. purchased equipment for $736,400 which was estimated to have a useful life of 10 years with a salvage value of $10,400 at the end of that time. Depreciation has been entered for 7 years on a straight-line basis. In 2015, it is determined that the total estimated life should be 15 years with a salvage value of $4,000 at the end of that time. (a) Prepare the entry (if any) to correct the prior years depreciation. (b) Prepare the entry to record depreciation for 2015.