help me answer exercise 4

Exercise 4 As part of an internal audit, the following facts were discovered by company's accountants. The audit occurred at the end of December 2015 before any adjusting entries or closing entries were prepared. a. Asset P was purchased January 2, 2012. It originally cost 540,000 and, for depreciation purposes, the straight-line method was originally chosen. The asset was originally expected to be useful for 10 years and have a zero residual value. In 2015, the decision was made to change the depreciation method from straight-line to sum-of-the-years- digits, and the estimates relating to useful life and residual value remained unchanged. b. Asset Q was purchased January 3, 2011. It originally cost 180,000 and, for depreciation purposes, the straight-line method was chosen. The asset was originally expected to be useful for 15 years and have a zero residual value. In 2015, the decision was made to shorten the total life of this asset to 9 years and to estimate the residual value at 3,000. c. Asset R was purchased January 5, 2011. The asset's original cost was 160,000, and this amount was entirely expensed in 2011. This particular asset has a 10-year useful life and no residual value. The straight-line method was chosen for depreciation purposes. d. At the end of 2014, the company failed to accrue 20,500 of commissions earned by employees during 2014. The expense was recorded when the commissions were paid in early 2015. Required Identify whether it represents an accounting change or an error for each situation above. If it is an accounting change, identify the type of change. Prepare any necessary journal entry as a direct result of the change or error correction as well as any adjusting entry for 2015 related to the situation described. (Ignore tax effects)