Problem 9-2 . O'Brien Company uses the perpetual inventory method O'Brien started the month of November with 500 units of inventory at a cost of $3 each. On November 5, O'Brien purchased 500 units at $5 each. On November 12, there was a sale of 400 units. On November 18, O'Brien purchased 500 units at $6 each. On November 25, there was a sale of 900 units. On November 29, O'Brien purchased 500 units at $9 each. All units were sold to customer for $14 each. . . . . 1. Use the following format to set up this.ioventory.costing problem, as shown in Video #2 Inventory Total Cost Date Units Cost per Date Units Total Cost Unit Beg Balance Units Cost Beginning Balance + Purchases 54 Goods Available for Sale - Sold Ending Balance 2. Use the FIFO cost assumption to calculate the cost of goods sold for each sale, the total cost of goods sold for the month and ending inventory. 3. Use the LIFO cost assumption to calculate the cost of soods sold for each sale, the total cost of eoods sold for the mooth and ending inventory. 4. Calculate O'Brien's gross margin Lising FIFO b. Usine LIFO a