Can someone please show me the step-by-step math for the first February 10th and the February 12th statement? Can't seem to figure it out. Thank you in advance!

Feb. 10: Sold merchandise inventory on account for $4,200. Payment terms were 1/15, n/30. These goods cost the company $2,100. Begin by preparing the entry to journalize the sale portion of the transaction. Do not record the expense related to the sale. We will do that in the following step. Date Accounts Debit Credit More Info - X Feb. 10 Accounts Receivable 4.158 Sales Revenue 4,158 Feb. Now journalize the expense related to the February 10 saleCost of goods, $2,100. Date Accounts Debit Credit 3 Purchased $3,700 of merchandise inventory on account under terms 3/10, n/EOM and FOB shipping point 7 Returned $700 of defective merchandise purchased on February 3. 9 Paid freight bill of $100 on February 3 purchase. 10 Sold merchandise inventory on account for $4,200. Payment terms were 1/15, n/30. These goods cost the company $2,100. 12 Paid amount owed on credit purchase of February 3, less the return and the discount 28 Received cash from February 10 customer in full settlement of their debt. Feb. 10 Cost of Goods Sold 2,100 Merchandise Inventory 2,100 Feb. 12: Paid amount owed on credit purchase of February 3, less the return and the discount. Print Done Date Accounts Debit Credit Feb. 12 Accounts Payable 3,000 Cash 2,910 Merchandise Inventory 90