I'm also struggling with this question: Find the maximum and minimum values by evaluating the equation C=4x-3y at the critical points if the restrictions are the following:

x is greater than or equal to 0, y is greater than or equal to 4, and x+y is less than or equal to 15.

The answer choices are:

a) minimum: -32 maximum: 45

b) minimum: -45 maximum: 32

c) minimum: -45 maximum: -32

d) minimum: 32 maximum: 45