Please help me solve Question E9-7 (A,B,C)

F9-7 Tones Company began operations on March 1, 2004. On that date, it purchased 400 items for inventory at a cost of $10 per unit. On March 14, Jones sold 200 units at $20 per unit. On March 16, 400 more units were purchased for inventory at a cost of $12 per unit. On March 21, Jones sold another 200 units at $20 per unit. bene Required: Assume that Jones Company uses a perpetual inventory system, Compute gross mar- gin for the month of March under LIFO and under FIFO. b. Repeat part (a) under the assumption that Jones uses a periodic inventory system. c. Why do your answers to parts (a) and (b) differ