please answer b and c thank you

An open box with a square base is to be made from a square piece of cardboard 21 inches on a side by cutting out a square from each corner and turning up the sides. See the figure. x Answers parts (a) through (e). 21 in -21 in. (a) Express the volume V of the box as a function of the length x of the side of the square cut from each corner. V = 4x - 84x + 441x (Simplify your answer.) (b) What is the volume if a 3-inch square is cut out? The volume is (Simplify your answer.) (c) What is the volume if a 9-inch square is cut out