Recording Purchases and Sales under Periodic and Perpetual Inventory Systems Demski Company reported beginning inventory of 600 units at a unit cost of $10. It engaged in the following purchase and sale transactions during 2017:
Jan. 14 Sold 120 units at unit sales price of $20 on open account.
April 9 Purchased 90 additional units at unit cost of $10 on open account.
Sept. 2 Sold 270 units at sales price of $25 on open account.
At the end of 2017, a physical count showed that Demski Company had 300 units of inventory still on hand.

Required:
Record each transaction, assuming that Demski Company uses 

(a) A periodic inventory system

(b) A perpetual inventory system (including any necessary entries at December 31, the end of the accounting period). Demski Company uses the FIFO inventory costing method.