Answer:
The amount Lava should charge against income during year 4 is $63,000.
Explanation:
Since amortization is assumed to be recorded at the end of each year, this can be calculated as follows:
Annual amortization expense = Cost of the patent / Patent's estimated useful life = $90,000 / 10 = $9,000
Amortization expense recorded prior to year 4 = Annual amortization expense * 3 years = $9,000 * 3 = $27,000
Unamortized cost of patent charge against income during year 4 = Cost of the patent - Amortization expense recorded prior to year 4 = $90,000 - $27,000 = $63,000
Therefore, the amount Lava should charge against income during year 4 is $63,000.