Sales transactions

Journalize the following merchandise transactions:

a$.$ Sold merchandise on account, $$18,000$ with terms $\frac{n}{30}.$ The cost of the goods sold was $$10,800.$ If an amount box does not require an entry, leave it blank.

b$.$ Received payment. If an amount box does not require an entry, leave it blank.

c$.$ Refunded $$600$ to customer for defective merchandise that was not returned. If an amount box does not require an entry, leave it blank.