Journalize the entries for the following transactions:
a. Sold merchandise for cash, $30,000. The cost of the merchandise sold was $18,000.
b. Sold merchandise on account, $120,000. The cost of the merchandise sold was $72,000.
c. Sold merchandise to customers who used MasterCard and VISA, $100,000. The cost of the merchandise sold was $70,000.
d. Sold merchandise to customers who used American Express, $45,000. The cost of the merchandise sold was $27,000.
e. Received an invoice from National Credit Co. for $9,000, representing a service fee paid for processing MasterCard, VISA, and American Express sales.