Answer:
a. The amount refund owed to the customer is : $29,792
b. To record the refund and the return of merchandise:
Dr Sales returned and Allowances     $30,400
 Cr Sales Discounts                              $608
 Cr Cash                                                $29,792
(to record the refund of $30,400 sales with sales discount of $608 made)
Dr Merchandise Inventory                    $13,060
 Cr Cost of Merchandise sold               $13,060
(to record the impact of the $30,400 sales refund on cost of merchandise sold and merchandise inventory) 
Explanation:
- Further explanation for sell discounts calculation:
As the terms is 2/10, total discount had been given as calculated below:
$30,400 x 2% = $608.