Z makes units that each requires 2 pounds of material at $3 per pound. 500 and 700 units will be built in May and June, respectively. Z keeps material on hand at 20% of the next month's production needs. How much is the material cost for May's output?
A. $2,400
B. $3,000
C. $3,240
D. $4,200
E. None of these