A rectangular piece of cardboard measuring 12 in by 18 in is to be made into a box by cutting equal size squares from each corner and folding up the sides. Let x represent the length of a side of each such square in inches. Complete parts (a) through (d) below. (a) Give the restrictions on x. (b) Determine a function V that gives the volume of the box as a function of x. (Round to the nearest hundredth.) (c) For what value of x will the volume be a maximum? (Round to the nearest hundredth.) (d)The volume will be greater than 80 cubic inches when (Type an integer or a decimal. Round to the nearest thousandth.)