Answer:
a. Using the cash basis of accounting: 
Cash received from customer $280,000 
Cash received for future service $12,000 
Total gross income $292,000 
b. Using the accrual basis of accounting:
Service revenue = ($280,000 - $40,000 + 60,000) = $300,000 
Gross income $300,000 
c) AI should use cash accural basis of accounting so that he will not have to pay income taxes on uncollected accounts receivable.