One hundred meters of fencing is available to enclose a rectangular area next to river give a function

Question

A that can represent the area that can be enclosed, in terms of X?

Answer 1

As solved previously:

Total fence length = 100 m
Total Length of each side perpendicular to river, W = X
Length of side parallel to river, L = 100-2X

Area,
A(X)= length * width
= L*W
= (100-2X)X

Simplify the right hand side to get the final solution.

Answer 2

100x-2x squared