You are designing a 18 cm3 right circular cylindrical can whose manufacture will take waste into account. there is no waste in cutting the aluminum for the side, but the top and bottom of radius r will be cut from squares that measure 3r units on a side. the total amount of aluminum used up by the can will therefore be upper a equals 18 r squared plus 2 pi rh, where h is the height of the right circular cylindrical can. what is the ratio of h to r for the most economical can?