Zephyr Minerals completed the following transactions involving machinery.

Machine No. 1550 was purchased for cash on April 1, 2023, at an installed cost of $52,900. Its useful life was estimated to be six years with a $4,300 trade-in value. Straight-line depreciation was recorded for the machine at the ends of 2023, 2024, and 2025.

On March 29, 2026, it was traded for Machine No. 1795, with an installed cash price of $62,000. A trade-in allowance of $30,210 was received for Machine No. 1550, and the balance was paid in cash. The fair values of Machine No. 1550 and Machine No. 1795 could not be determined.

Machine No. 1795’s life was predicted to be four years with a trade-in value of $8,200. Double-declining-balance depreciation on this machine was recorded each December 31. On October 2, 2027, it was traded for Machine No. BT-311, which had an installed cash price of $537,000, the machine’s fair value. A trade-in allowance of $20,000 was received for Machine No. 1795, and the balance was paid in cash.

It was estimated that Machine No. BT-311 would produce 200,000 units of product during its five-year useful life, after which it would have a $35,000 trade-in value. Units of production depreciation was recorded for the machine for 2027, a period in which it produced 31,000 units of product. Between January 1, 2028, and August 21, 2030, the machine produced 108,000 more units. On August 21, 2030, it was sold for $81,200.

Required

Round calculations to the nearest dollar and prepare journal entries to record:

a. The depreciation expense recorded to the nearest whole month on the first December 31 of each machine’s life.

b. The purchase/exchange/disposal of each machine.