- If x represents the length of the enclosed rectangular garden and w represents its width, then all 30 meters of fencing are used when 2x+2w=30. Simplifying makes x+w=15 so w=15−x. If A(x) represents the area of the enclosed rectangle as a function of x, thenA(x)=xw=x(15−x)=−x2+15xFind the x-coordinate of the vertex:x=−2ab​=−2(−1)15​=7.5The maximum value of A(x) occurs at x=7.5 :A(7.5)​=−(7.5)2+(15)(7.5)=−56.25+112.5=56.25 m2​The correct choice is (B).