E8-7 Recording Purchases and Sales Using a Perpetual and Periodic Inventory System Demski Company reported beginning inventory of 100 units at a unit cost of $25. It engaged in the following purchase and sale transactions during 2007: Jan. 14 Sold 25 units at unit sales price of $40 on open account. April 9 Purchased 15 additional units at unit cost of $25 on open account. Sept. 2 Sold 50 units at sales price of $45 on open account. At the end of the 2007, a physical count showed that Demski Company had 40 units of inventory still on hand. Required: Record each transaction, assuming that Demski Company uses (a) a perpetual inventory system and (b) a periodic inventory system (including any necessary entries at December 31, the end of the accounting period)