A farmer divides a rectangular piece of land into 8 equal-sized rectangular sheep pens as shown in the diagram.

Each sheep pen measures x m by ym and is fully enclosed by metal fencing. The farmer
uses 480 m of fencing.

(i) Show that the total area of land used for the sheep pens, A m², is given by
A = 384x-9.6x².

(ii) Given that x and y can vary, find the dimensions of each sheep pen for which the value of A is a maximum. (There is no need to verify that the value of A is a maximum.)