To determine what the depreciation of an asset using straight line method, the formula to be used is:
(Initial cost of machine – salvage value) divided by estimated useful life
So in this problem:
Initial Cost - $135000
Salvage Value – $15000
Estimated Useful Life – 5 years
Plug that in the formula
Annual depreciation = ($135000 - $15000) / 5
= $120000/ 5
= $24,000
The first year depreciation for the machine is $24000 because the company bought it in the beginning of the year. (So there is no need to divide this by 12 months)
To record this:
Depreciation Expense $24000
Accumulated Depreciation $24000