The answer is 5.5 feet.
15.125= 1/2 * b* h
15.125= 1/2 * b* (5.5)
2(15.125)= 2 (1/2 * b *(5.5))
30.25= b * 11
30.25/11= b * 11/11
2.75 = b
You have to check it so when you plug the solved variable back in
15.125= 1/2 * (2.75) * (5.5)
15.125= 7.5625
So because the original b variable does not equal to the area of the triangle, you multiply the b variable by two to get 5.5 and when you plug that in, you get 15.125.