First off, you're going to end up with 2 answers.
Alright so you have:

You'll want to multiply both sides by b²
You'll end up with:

Multiply both sides by

Now you should have:

Subtract 750b^2 from both sides.
Now:

Factor the left side of the equation:

Set both factors to 0:

Your Answers:
b = 0 or b = 