Answer:
The book value at the end of the third year is $8640.
Explanation:
Book value at end of year = Original Cost - Accumulated Depreciation
The automobile cost is $30000.
After 1st year, the depreciation will be =

After 2nd year the depreciation will be =
dollars
Similarly after 3rd year the depreciation will be =

Now, adding all the depreciation amounts:
dollars
Book Value at end of year =
dollars
Therefore, the book value at the end of the third year is $8640.