math hw help needed asap

Question

A gardener has 520 feet of fencing to fence in a rectangular garden. One side of the garden is bordered by a river and so it does not need any fencing.

  

What dimensions would guarantee that the garden has the greatest possible area? 

shorter side:   ft (feet)

longer side:  ft (feet)

greatest possible area:   ft²  (square-feet)

Answer 1

W rerpresents that width of the garden.

520 - 2W represents the length.

W(520 - 2W) = A(W)

Can you conver to vertex form and answer?