Anybody know how to do this

Enclose a rectangular plot with 280 m of fencing so that the length is twice the width and the area is divided into two equal parts. Find the length and the width of the lot.
The book says the answer is 40 m x 80 m.

Let x = width. Therefore, length = 2x

The perimeter is 2x + x + 2x + x (=6x). You will also use another x length to divide the plot in half.

So you need 7x metres of fencing and you have 280m available.

7x = 280
x = 280/7 = 40

Answer: width = x = 40m, length = 2x = 80m

L = Length W = Width
L = 2W
280 = 2L + 3W (extra W to divide the field into 2)
280 = 4W+3W = 7W
W = 40 m
L = 80 m

3W+2L = 280 (3W because of the extra W that divides it in half)
L = 2W
W=40
L=80