[The following information applies to the questions displayed below.] Fraud Investigators Inc. operates a fraud detection service. a. On March 31, 10 customers were billed for detection services totaling $30,000. b. On October 31, a customer balance of $1,750 from a prior year was determined to be uncollectible and was written off c. On December 15, a customer paid an old balance of $850, which had been written off in a prior year. d. On December 31, $550 of bad debts were estimated and recorded for the year