Al is a medical doctor who conducts his practice as a sole proprietor. During 2021, he received cash of $604,000 for medical services. Of the amount collected, $43,200 was for services provided in 2020. At the end of 2021, Al had accounts receivable of $89,700, all for services rendered in 2021. In addition, at the end of the year, Al received $18,000 as an advance payment from a health maintenance organization (HMO) for services to be rendered in 2022. a. Compute Al's grass income for 2021 using the cash basis of accounting. M b. Compute Al's gross income for 2023 using the accrual basis of accounting