June Corp. sells one product and uses a perpetual inventory system. The beginning inventory consisted of 20 units that cost $20 per unit. During the current month, the company purchased 120 units at $20 each. Sales during the month totaled 90 units for $43 each. What is the cost of goods sold using the LIFO method? a. $400 b. $1,800 c. $2,400. d. $3,870