You work at Dave's Donut Shop. Dave has asked you to determine how much each box of a dozen donuts should cost. There are 12 donuts in one dozen. You determine that it costs $0.32 to make each donut. Each box costs $0.18 per square foot of cardboard. There are 144 square inches in 1 square foot. Whats an expression to model the number of donuts in b boxes?

A box of donuts would cost: b = 3.84 + 0.18f

First, we have to find the total cost of the donuts. 
12 x 0.32 = 3.84

Next, we need to determine the cost of the box. However, we don't know the surface area, just the cost per foot. We can multiply the number of square feet of the box by $0.18 to find the cost.

So our equation could be:  b = 3.84 + 0.18f (where f is the surface area of the box in square feet)