A 3000 payment for repairs was erroneously charged to the

Question

The following income statement was prepared for Cool Pool Supplies for the year 2013:

COOL POOL SUPPLIES
Income Statement
For the Year Ended December 31, 2013
Sales ................$280,000
Cost of goods sold .........$ 155,000 
Gross margin ............$ 125,000
Operating expenses .........$ 81,200 
Net income .............$ 43,800

During the year end audit, the following errors were discovered:

1. A $3,000 payment for repairs was erroneously charged to the Cost of Goods Sold account.  Assume that the perpetual inventory system is used.  

2. Sales to customers for $1,500 at December 31, 2013, were not recorded in the books for 2013. Also, the $900 cost of goods sold was not recorded. The error was not discovered in the physical count because the goods had not been delivered to the customers. 

3. A mathematical error was made in determining ending inventory. Ending inventory was understated by $2,350.  The Inventory account was mistakenly written down to the Cost of Goods Sold account. 
Required: Determine the effect, if any, of each of the errors on the following items. Give the dollar amount of the effect and whether it would overstate  O , understate  U , or not affect  NA  the account.

The first item for each error is recorded as an example.