Answer:
The side needs a fence that is longer than 3 ft. and shorter than 13 ft.
Explanation:
We are given backyard to enclose a garden in form of a triangle.
First side 'x' = 8 feet.
Second side 'y' = 5 feet
Third side = z
Property of triangle : the third side must be smaller than the sum of the other two sides but greater than their difference


So, third side must be shorter than 13 feet


So, third side must be longer than 3 feet
Hence option B is correct :The side needs a fence that is longer than 3 ft. and shorter than 13 ft.