If you could show what math is done to get the answers that would be very helpful, Thanks!

At the beginning of July, CD City has a balance in inventory of $2,400. The following transactions occur during the month of July July 3 July 4 July 9 July 11 July 12 July 15 July 18 July 22 July 28 July 30 Purchase CDs on account from Wholesale Music for $1,300, terms 1/10, n/30 Pay freight charges related to the July 3 purchase from Wholesale Music, $120 Return incorrectly ordered CDs to Wholesale Music and receive credit, $200 Pay Wholesale Music in full. Sell CDs to customers on account, $3,800, that had a cost of $2,000 Receive full payment from customers related to the sale on July 12. Purchase CDs on account from Music Supply for $2,100, terms 1/10, n/30 Sell CDs to customers for cash, $3,200, that had a cost of $1,500 Return CDs to Music Supply and receive credit of $100 Pay Music Supply in full