I was given the question-- ABC Company agreed upon a ten-month, $18,000, 4% interest-bearing note receivable from XYZ Corporation on April 1, 2009 for a sale of a piece of equipment. In other words, ABC gave XYZ the equipment in exchange for a longer-term receivable. Assuming all necessary adjusting entries were made at year end December 31, 2009 and interest will be received upon maturity, the entry ABC makes on the note's maturity date would include a:

(a) credit to interest receivable for $540

(b) credit to note payable for $18,000

(c) debit to interest revenue for $60

(d) debit to interest expense for $600

The answer is (a) credit to interest receivable for $540. Could someone help me understand why that is the answer? I understand why $540 is correct but not the credit to interest receivable part.