need help on this question. I tried using the (purchase-return-discount) but keep getting the wrong answer

Freight Terms Determine the amount to be paid in full settlement of each of two invoices, (a) and (b), assuming that credit for returns and allowances was received prior to payment and that all invoices were paid within the discount per ad. If required. round the answers to the nearest dollar. Freight Paid by Seller Credit for Refunds and Allowances Merchandise Freight Terms $500 $1,400 FOB shipping point, 1/10, n/30 $9,000 a 750 b 3,800 FOB destination, 2/10, n/30 400 a. $ b. Feedback Check My Work a & b. Under FOB shipping point, freight is paid by the buyer, while under FOB destination freight is the seller's expense. To determine the amount, first deduct the return before calculating the discount. Then calculate (Purchase - Return - Discount) + applicable freight