Intermediate algebra problem

I need help solving this. I just can't figure it out. [(4/ab)-(3/b^2)]/[(5/a)(3/b^2)]

Step 1: Use rules for adding and subtracting fractions to find a simpler expression for the numerator.
4/(ab) - 3/(bb) = 4b/(abb) - 3a/(abb) = (4b - 3a)/(abb)

Step 2: Use rules for multiplying fractions to find a simpler expression for the denominator.
5/a * 3/(bb) = (5*3)/(a*bb) = 15/(abb)

Step 3: Use rules for dividing fractions to find a simpler expression for the fraction.
[(4b - 3a)/(abb)]/[15/(abb)] = (abb)/15 * (4b - 3a)/(abb)
= (abb)/(abb) * (4b - 3a)/15
= (4b - 3a)/15 when a and b are not zero. The expression is undefined if a or b equals zero, because 0/0 is indeterminate.