WT Ltd uses the perpetual inventory system. Below is an analysis of the inventory purchases and sales for 2021: Purchases Sales Units Unit Cost Units Selling Price/Unit Jan. Opening inventory 40 200 Mar. Purchase 60 220 Apr. Sales 60 380 Jul. Purchase 230 Nov. Sales 30 400 20 Required: Calculate the cost of goods sold, closing inventory and gross profit under each of the following methods: 1) 2) First-in, First-out (FIFO); and Weighted average cost (WAC)