Help with accounting problem.

I think I got the first part correct and need help with part B. Please explain details for me. Thank you. If there are mistakes in part A please let me know also. Thank you

problem:

On January 1, 2017, Reese Dyno Tune Company purchased a shop building and Hi-tech Dyno Tune Equipment that had the following useful lives, salvage value, and costs.

Shop Building, 20-year estimated useful life, $575,000 cost, $100,000 salvage value

Hi-tech Dyno Tune Equipment, 10-year estimated useful life, $130,000 cost, and a salvage value of $20,000.

The building has been depreciated using the straight-line method for the years 2017, 2018, and 2019. In 2020, the company decided that due to the wear and tear on the building and its limitations in size, its original estimated total useful life should be 15 years and not 20 years as originally estimated. In addition, it is also estimated that the salvage value will be zero.

The company also decided to change the total useful life of the machinery to 6 years, with a salvage value of $5,000 at the end of that time. The equipment has been depreciated using the sum of the years digit method for 2017, 2018, and 2019. The company will now depreciate the equipment using straight-line beginning in 2020.

Instructions

(a)Calculate 2020 depreciation expense and prepare the journal entry necessary to record the depreciation expense on the shop building in 2020.

(b)Calculate depreciation expense on the Hi-tech Dyno Tune Equipment for 2020 and prepare the journal entry for 2020.

Answer I have so far:

A. Straight line depreciation - ($575,000 - 100,000) = 475,000 / 20 = 23,750 per year

23,750 x 3(years 2017,2018,2019) = 71,250

Cost of Shop building	$575,000
Less: Salvage value	100,000
	475,000
Less: Depreciation first 3 years	71,250
Remaining book value (no salvage value 2020 add 100,000 back)	503,750
Remaining Book value: 403,750 / 12(years)	41,979.16
Per year deprecation 2020	41,979.16

Date	Accounts	Dr	Cr
2020	Depreciation expense	$41,979.16
	Accum Depreciation		$41,979.16

B.