So take 3 x 1/2 = 1 1/2 cups. Now we know that we need 1 1/2 cups of lemon juice. So convert 1 1/2 cups into tbsp and you get 24 tbsp. Now since 1 lemon is equal to 2 tbsp divide the 24 tbsp by 2 and you get 12. This 12 represents the amount of lemons you need to buy. Since 1 lemon is $0.66 take that and multiply it by the amount of lemons you need (12x0.66) now you get $7.92.
You need $7.92 to but 12 lemons to make three 9 inch lemon pies.