Rational Equations with expressions in the denominator

[csmith035]

This is the question and my answer

10b-50/b^2-b-20 divided by 15/6b+24

I got 10(b-5)/(b+4)(b-5)x 6(b+4)/15

i marked the (b+4) off

im left with

10(b-5)/(b-5)x6/15