An open rectangular box (no top) with a volume 9 cubic meters has a square base. The base has side x m. The equation of surface area of the box is x2 + 36/x.
The base costs 1 cents/square m and the sides cost 1.6 cents/square m. I found the expression for the cost as a function of x to be x2 (1) + 57.6/x.
I can't figure out how to calculate the value of x to achieve minimum cost??? It has to be calculated with the second derivative test.