Answer and Explanation:
The journal entries are shown below:
Cash Dr $15,000
 To Sales $15,000
(Being cash is recorded)
Cost of goods sold Dr $9,000
 To Merchandise inventory $9,000
(being cost of the merchandise is recorded)
Sales returns & allowances $1,290
 To Cash $1,290
(being sales return is recorded)
 Merchandise inventory ($1,290 × $9,000 ÷ $15,000) $774
 To Cost of goods sold $774
(being merchandise inventory is recorded)