Hi, this kind of problems involves the use of properties. So you want that expression to be simplified in one logarithm.
First, let's write everything as a logarithm. We know that: so we could say that (in our case). Thus
Then, we have to put, for the second part, "inside" the logarithm. So we also know that: . Finally
We put it altogether (using the substraction of logarithm property of the same base) :