Divide 1-125b^3 by 5b - 1
You need to learn the technique of polynomial long division. It's just the same as if numbers were involved.
See http://www.sosmath.com/algebra/factor/fac01/fac01.html
for sevaral examples.
Hint: It will be a three-term polynomial. The first term will be
25 b^2 and the last term will be 1