For W to be maximum ; \\\\(\\dfrac{dW}{dx} = 0\\\\);i.e. \\\\( F(x) = 0 \\Rightarrow x= l, x = 0\\\\)clearly for \\\\(d = l \\\\), the work done is maximum.Alternate Solution :External force and displacement are in the same direction\\\\(\ herefore\\\\) Work will be positive continuously so it will be maximum when displacement is maximum.