please answer bottom two questions

An open box with a square base is to be made from a square piece of K cardboard 21 inches on a side by cutting out a square from each corner and turning up the sides. See the figure. Answers parts (a) through (e). 21 in. X X -21 in. Xmin = 0, Xmax = 10.5, Xmin =0, Xmax = 10.5, Xmin = 0, Xmax = 10.5, Xmin = 0, Xmax = 10.5, Xscl = 0.5, Ymin = 0, Xsel = 0.5, Ymin = 0 Xsel = 0.5. Ymin = 0. Xscl = 0.5, Ymin = 0. Fn For what value of x is V largest? X = inches (e) What is the largest volume? The largest volume is cubic inches