Can someone solve this problem with EXPLANATION one by one??

Alpha, Inc., made errors and/or omissions during the current year as described below. Indicate the effect of these errors and omissions on total assets, total liabilities, and net income for the year using the following code: O = overstated, U = understated, N = no effect. Alpha uses a periodic inventory system and a year ending December 31. Ignore income taxes.

1. Alpha failed to record the following AJE: The Sales account includes a $5,000 payment received in advance from a customer. By year-end, only $3,000 of the merchandise had been delivered to the customer.

2. Alpha failed to record the return of merchandise to its supplier (vendor) for cash. Assume the use of the periodic inventory system.

3. Failed to record AJE: Examining the Rent Expense account, the controller finds that it includes a $4,800 advance payment for 3 months rent. The payment was made on November 1.