Tell me the dimensions and the maximun total area

Question

A rancher has 320  feet of fencing to enclose two adjacent rectangular corrals.

a)What dimensions will produce the largest total area? (separate by commas)

b) What is the maximum total area? 

Answer 1

320 = 2L + 3W

2L= 320-3W

L = 160 -3W/2

Area = A = LW = (160-3W/2)W = 160W -3W^2/2

A' = 160 -3W = 0

3W = 160

W = 160/3= 53 1/3 feet wide

L=160 -(3/2)(160/3) = 80 feet long

3(160/3) + 2(80) = 320 total feet of fencing

max area = 160/3 x 80 = 4,266 2/3 square feet