Functions of several cariables - minimum cost

[glitchy]

A closed rectangular bos with a volume of 16cu. ft is made from 2 kinds of materials. the top and bottom are made of material costing 10cents per square foot and the sides of the material costing 5censts per sqaure foot. what r the dimenstions of the box so that the cost of the materials is minimized.

How do I go about starting this.

I was able to solve a similar one regarding maximizing the volume of a box, nothing with cost though.

any help is appreciated.

 

[Dick]

Write an equation for the cost of the box in terms of the three dimensions. Use the fixed volume of the box to eliminate one of the variables. Then set the partial derivatives of the cost with respect to the two remaining variables equal to zero. The result should be two equations in two variables. Et voila.