an open top box is to be constructed by cutting out squares from each corner of a 14 cm by 20 cm sheet of plastic then folding up the sides express

an open top box is to be constructed by cutting out squares from each corner of a 14 cm by 20 cm sheet of plastic then folding up the sides express the volume of the box as a polynomial function in terms of x. what value of x maximizes the volume enclosed by the box