Joe Leung, CPA, is auditing Louie's Wholesalers Ltd. (Louie)'s financial statements and is about to perform substantive audit procedures on Louie's Wholesalers Ltd.'s trade accounts payable balances. After obtaining an understanding of Louie's internal controls for the purchasing process, Joe Leung assessed control risk below the maximum. Joe Leung requested and received from Louie a schedule of the trade accounts payable prepared using the trade accounts payable subsidiary ledger. Required: (a) Discuss how the use of pre-numbered documents serve as an internal control. (b) Briefly describe each of the following documents or records: purchase requisition; purchase order; receiving report, supplier invoice; and voucher. Why would a company combine all these documents related (6 mark (12 mark Rege 3 of to a purchase transaction into a "voucher packet/package"? (c) Describe six (6) substantive audit procedures Joe Leung should apply to Louie's trade accounts payable balances. (12 marks)