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 paid cash dividends to its shareholders but erroneously recorded one of the dividend payments as satisfying an account payable.

2. Alpha sold merchandise to Beta on credit with terms F.O.B. Destination. As of December 31, the merchandise had not yet been received by Beta. Alpha recorded the sale and did not count the merchandise in ending inventory (periodic system).

3. Alpha purchased merchandise on credit with terms F.O.B. Destination. As of December 31, the merchandise had not yet been received by Alpha. Alpha recorded the purchase and included the merchandise in ending inventory (periodic system).

4. Alpha failed to record the return of inventory to the manufacturer for a credit (periodic inventory system).