On June 30th Gamma Inc. sold finished goods to a customer for 25,000. The customer signed a 9-month note at 5% yearly interest. On the maturity date, the customer did not pay, so Gamma billed him for the full amount of the dishonoured note. Gamma at the same time recorded an allowance for doubtful accounts of 3,500. After a few unsuccessful collection attempts, the customer eventually paid 15,500.

How do I journalize this?