Penn Company is in the process of adjusting and correcting its books at the end of 2017. In reviewing its records, the following information is compiled. 1. Penn has failed to accrue sales commissions payable at the end of each of the last 2 years, as follows.

December 31, 2016 $3,500
December 31, 2017 $2,500

2. In reviewing the December 31, 2017, inventory, Penn discovered errors in its inventory-taking procedures that have caused inventories for the last 3 years to be incorrect, as follows.

December 31, 2015 Understated $16,000
December 31, 2016 Understated $19,000
December 31, 2017 Overstated $6,700

Penn has already made an entry that established the incorrect December 31, 2017, inventory amount.

3. At December 31, 2020, Penn decided to change the depreciation method on its office equipment from double-declining-balance to straight-line. The equipment had an original cost of $100,000 when purchased on January 1, 2018. It has a 10-year useful life and no salvage value. Depreciation expense recorded prior to 2017 under the double-declining-balance method was $36,000. Penn has already recorded 2017 depreciation expense of $12,800 using the double-declining-balance method.
4. Before 2017, Penn accounted for its income from long-term construction contracts on the completed-contract basis. Early in 2017, Penn changed to the percentage-of-completion basis for accounting purposes. It continues to use the completed-contract method for tax purposes. Income for 2017 has been recorded using the percentage-of-completion method. The following information is available.

Required:
Prepare the journal entries necessary at December 31, 2017, to record the above corrections and changes.