Answer:
4 years
Step-by-step explanation:
Given;
Purchasing cost of the vehicle = $50,000
Salvage value = $10,000
Depreciation expense = $5,000
Depreciation account at the end of the current year = $20,000
Now,
Annual Depreciation expense using the straight-line method is given as;
=

=

or
Depreciation expense =

also,
Depreciation expense = $5,000
thus,
$5,000 =

or
useful life =

or
useful life = 4 years