Answer:
Step-by-step explanation:
Area of a rectangle = Length x Breadth.
Area= L x B
We are told the length is twice the breadth.
You can write this as :
Length = 2 x Breadth
L = 2B
If you put that into the area formula at the beginning, we get:
Area = L x B
Area = 2B x B = 
They also told us that the area of the field is 3200 square meters. So,
Area =
= 3200
Divide both sides by 2
= 
Now to solve for B we need to square root both sides.
= 40
So now we know the Breadth is 40meters
Remember earlier we said Length = 2 x Breadth

Cost of fencing the field = 2L + 2B
Cost of fencing the field = 2 x 80 + 2 x 40 = $240