You are asked to find the minimal cost of materials to construct a rectangular storage container with an open top having a volume of 10 m3. The length of the base is twice the width. Material for the base cost 15 per square meter, and material for the sides costs 5 per square meter. Let C represent the cost, w the width of the box, l the length of the box, and h the height of the box. Required:
Write down the equation that should optimize to find the minimal cost of materials to construct the box.