1. On March 31, 10 customers were billed for detection services totaling $29,000.

2. On October 31, a customer balance of $1,700 from a prior year was determined to be uncollectible and was written off.

3. On December 15, a customer paid an old balance of $860, which had been written off in a prior year.

4. On December 31, $540 of bad debts were estimated and recorded for the year.

5. i need help understanding these