3 cans of green beans cost $1.80 retail but 9 cans of green beans how much did he pay

Let us see if I understand the question:

3 cans of green beans cost $1.80 retail but (a man bought) 9 cans of green beans how much did he pay?

Well, $1.80 divided by 3 = $0.60 per can

and, 9 cans cost $0.60 per can. 9 times $0.60 = $5.40