Answer: $8000
Explanation: Under straight line method of depreciation, the book value of an asset is spread over its useful life . It can be computed using following formula :-
[tex]=\:\frac{Initial cost\:-\:salvage\:value}{useful\:life}[/tex]
putting the values into equation we get,
[tex]=\:\frac{50,000\:-\:10,000}{5}[/tex]
therefore,
depreciation expense = $8000