Answer:
Journal entries 
Step-by-step explanation:
The journal entries are as follows
 On Sep 6
Merchandise Inventory $ 1,600
 To Accounts Payable $1,600
(Being the merchandise inventory is purchased on account)
 On Sep 9
Merchandise inventory Dr $40
 To Cash $40
(Being freight is paid by cash)
 On Sep 10 
Cash Dr $50
 To Merchandise inventory $50
(Being returned inventory is recorded) 
On Sep 12
 Accounts receivable Dr $600
 To sales $600
(Being calculators sold at sale price) 
Cost of goods sold Dr $450
 To Merchandise inventory $450
(Being calculator sold at cost price) 
On Sep 14 
Sales return and allowance Dr $35
 To Accounts receivable $35
(Being sales return is recorded) 
Merchandise inventory Dr $25
 To Cost of goods sold $25
(Being sales return is recorded) 
On Sep 20 
Accounts receivable Dr $650
 To sales $650
(Being calculators sold at sale price) 
Cost of goods sold Dr $500
 To Merchandise inventory $500
(Being calculator sold at cost price)