Question

(1 pt) A rectangular storage container with an open top is to have a volume of 10 \mbox{ m}^3. The length of its base is twice the width. Material for the base costs 10 dollars per square meter. Material for the sides costs 6 dollars per square meter. Find the cost of materials for the cheapest such container. Let \ell denote the length of the base, w the width of the base, and let h denote the height of the container. First, write an equation for the cost of the materials in terms of \ell, w, and h. I'm confused on how to find the cost formula