Required information (The following information applies to the questions displayed below.) Fraud Investigators Incorporated operates a fraud detection service. a. On March 31, 10 customers were billed for detection services totaling $27,000. b. On October 31, a customer balance of $1,600 from a prior year was determined to be uncollectible and was written off. c. On December 15, a customer paid an old balance of $880, which had been written off in a prior year. d. On December 31, $520 of bad debts were estimated and recorded for the year. Required: 1. Prepare journal entries for each transaction above. (If no entry is required for a transaction/event, select "No Journal Entry Required" in the first account field.)