Problem
Mar wants to make a box with no lid from a rectangular sheet of cardboard that is 18 inches by 24 inches. The box is to be made by cutting a square of side x from each corner of the sheet and folding up the sides. Find the value of x that maximizes the volume of the box.
Problem 19
A druggist sells a certain kind of powder in a rectangular box 4 by 2 by 1 in. for 25 cents, and in a cylindrical can 2½ in. high and 2½ in. in diameter for 10 cents. Which is the more economical buy?