Al is a medical doctor who conducts his practice as a sole proprietor. during 2017, he received cash of $280,000 for medical services. of the amount collected, $40,000 was for services provided in 2016. at the end of 2017, al had accounts receivable of $60,000, all for services rendered in 2017. in addition, at the end of the year, al received $12,000 as an advance payment from a health maintenance organization (hmo) for services to be rendered in 2018.compute al's gross income for 2017: