The following are independent errors:
a. In January 2019, repair costs of $9,000 were debited to the Machinery account. At the beginning of 2019, the book value of the machinery was $100,000. No residual value is expected, the remaining estimated life is 10 years, and straight-line depreciation is used.
b. All purchases of materials for construction contracts still in progress have been immediately expensed. It is discovered that the use of these materials was $10,000 during 2018 and $12,000 during 2019.
c. Depreciation on manufacturing equipment has been excluded from manufacturing costs and treated as a period expense. During 2019, $40,000 of depreciation was accounted for in that manner. Production was 15,000 units during 2019, of which 3,000 remained in inventory at the end of the year. Assume there was no inventory at the beginning of 2019.

Required:
Prepare journal entries for the preceding errors discovered during 2020. Ignore income taxes.