Answer:
b.

Explanation:
We are given that
Gabriella's father gave her fencing of length =90 feet
Length of each side of two equal side =15 feet
Let length of each side of other two equal sides=r
We have to find the equation which represents the best situation.
Perimeter of rectangle =

Perimeter of rectangular enclosure=length of fencing
Using the formula


Hence, the required equation which represents the situation best is given by

Option b is true.