4. 8 marks An open topped box is to be made by cutting out identical squares from the corners of a rectangular piece of cardboard then folding up the resulting flaps. Thus, if the side of each removed square has length a then the box height will also be r. If the cardboard has dimensions 70cm by 50cm find an expression for the volume of the box V(x) in terms of r. What is the domain of this function? What sort of function is it (quadratic, cubic, rational or. ..)?