Hi,

I just started taking a Pre-Calculus math course in College. I took this course years ago and since then have forgotten most of what I have learned. I have come across the following question which I am stuck on.

A box with a square base has a volume of 600 cubic cm. If the material for the 4 sides and the top costs 5 cents per square cm and the material for the reinforced base costs 10 cents per square cm, express the total cost C of material (in cents) as a function of x, where x is the length of a side of the square base. Write the function in simplified form.

I have gotten this far:

Area =

Area =

The answer that is given to me is

I can see that if I multiply the 2400 by 5 I will get the but I don't understand where the comes from.