Casey consumes two goods, hamburgers and ice cream sandwiches. he has maximized his utility given his income. ice cream sandwiches costs $2, and he consumes them to the point where the marginal utility he receives is 6. hamburgers cost $4, and the relationship between the marginal utility that casey gets from eating hamburgers and the number he eats per month is as follows:

hamburgers 1 2 3 4 5 6
marginal utility 20 16 12 8 4 0

how many hamburgers does casey buy each month?

a) 1
b) 2
c) 3
d) 4