Fraud Investigators Incorporated 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