Chess Top uses the periodic inventory system. For the current month, the beginning inventory consisted of 480 units that cost $65 each. During the month, the company made two purchases: 720 units at $68 each and 360 units at $70 each. Chess Top also sold 1,200 units during the month. Using the LIFO method, what is the amount of cost of goods sold for the month?

The answer is 81960, but i don't know how to get this answer.