How do you solve this problem?

A billboard designer has decided that a sign should have 4-ft margins at the top and bottom and 1-ft margins on the left and right sides. Furthermore, the billboard should have a total area of 6400 ft2 (including the margins). Printed Region 8 If x denotes the left-right width (in feet) of the billboard, determine the value of x that maximizes the area of the printed region of the billboard. X = x feet Use this value of x to compute the maximum area of the printed region. Maximum area of printed region = 5616 x square feet