Therefore: DC=AB=xm, DC‖AB.
Therefore: △EDC∽△ EAF.
Therefore: DC/AF=ED/AE.
AE = 30m,AF = 40m。
So: x/40 = (AE-ad)/AE.
Therefore: x/40 = (30-ad)/30.
Therefore: AD = 30-3/4x
(2)y=AB? AD=x(30-3/4x)
So: y=-3/4(x-20)? +300
So when x takes 20, the value of y is the largest. The maximum value is 300.