a. Dec. 1 - business receives $6,600 for a 10 -month service contract. Dec. 31 - year-end adjusting entry needed to update the balance in the account. b. Mar. 31 - work performed but not yet billed to customers for the month, $1,000. Apr. 21 - received payment for the work that was completed. c. Jun. 15 - purchased $3,300 of office supplies on account. Dec. 31 - a count of supplies shows that only $1,200 worth is left at year-end, so the balance in the account needs to be updated. d. Feb. 2 - business paid a $900 deposit for the last month's rental of a copier on a 10-month contract Nov. 30 - the rental period for the copier ended, so the balance in the prepaid account must be updated. e. Jun. 1 - purchased truck for $30,600 (cash) with an expected useful life of six years. Dec. 31 -year-end adjusting entry needed to record amortization