A rectangular sheet of width x cm is to be folded into a tray. Two equal strips of width x cm are cut from a cardboard of length 20 cm so that the new length becomes (20−2x) cm while the width remains x cm.
(i) Write the area A(x) of the tray as a polynomial in x.
(ii) For what positive value of x (other than 0) does the area become zero?