The answer would be -15.74
I'm pretty sure you are asking for the value of b. Let's actually write it and then solve it:

Solving for b yields:

So,
b = 19.59. If you want the answer in simplified radical form, we can also do that:

So,
b = 8√6 = 19.59
100 hahahhahah yk what he
81 cent.........................................................