Since both fractions have the same denominator, we just need to subtract the numerators:

Notice that we have a common factor, 3, in the numerator, so lets factor that out:

Next, we can factor the denominator:

Now we can cancel the common factor

in both numerator and denominator:
We can conclude that the result of 3h/h^2-12h+36 -18/h^2-12h+36 is:
