A rectangular box is to have a square base and a volume of 80 fts . If the material for the base costs 15 cents per square foot, material for the top costs 35 cents per square foot, and the material for the sides costs 20 cents per square foot, determine the dimensions of the square base (in feet) that minimize the total cost of materials used in constructing the rectangular box. O 4-by-4 O 2-by-2 O 5-by-5 8-by-8 O 6-by-6