Answer:
b.
![90=30+2r](https://img.qammunity.org/2020/formulas/mathematics/middle-school/c6vc4sj2ufnysvtiupidt29lwthn85wbg9.png)
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 =
![2(l+b)](https://img.qammunity.org/2020/formulas/mathematics/college/hfq8g0bvhttb2jtxarw1wzkno75gr7p6g1.png)
Perimeter of rectangular enclosure=length of fencing
Using the formula
![90=2(15+r)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/u8rulygjkbhkiqp9vtuzz3vpgb7r2t960u.png)
![90=30+2r](https://img.qammunity.org/2020/formulas/mathematics/middle-school/c6vc4sj2ufnysvtiupidt29lwthn85wbg9.png)
Hence, the required equation which represents the situation best is given by
![90=30+2r](https://img.qammunity.org/2020/formulas/mathematics/middle-school/c6vc4sj2ufnysvtiupidt29lwthn85wbg9.png)
Option b is true.