please explain

(21 Prepare journal entries for the following independent transactions. a. Erratic Corp. traded in several old computers for two new computers at the beginning of April. After updating depreciation prior to the trade-in, the Accumulated Depreciation account had a balance of $5,300 and the original cost of the computers was $10,900. In addition, Erratic Corp. paid $5,000 to acquire the new computers. b. Terrain Corporation sold office equipment for $10,000 cash. The original cost of the equipment was $15,000; accumulated depreciation up to the date of sale had a balance of $6,900 c. Glacial Limited disposed of fully amortized office furniture. The office furniture had a cost of $10,200 and no residual value