For each transaction below, calculate the amount of revenue to be recorded in the current period using accrual$-$basis accounting:

Required:

a$.$ Performed $$29,000$ of services during the month and received full cash payment from customers at the time of service.

b$.$ Performed $$8,000$ of services during the month and billed customers. Customers are expected to pay next month.

c$.$ Received $$13,000$ cash from customers for services to be provided next month.