We want to simplify the expression:

We could simplify this equation factoring its denominator and its numerator.
First, let's factor the numerator as follows:

Start multiplying and dividing the equation by 6 and then re-write it as:

Now, we're going to ask two numbers, whose sum is -24 and its multiplication is 144.
These numbers are -12 and -12. We can put these numbers in our previous equation like this:

Now, we could apply common factor to this expression:

And, we're going to simplify the denominator of the rational expression applying common factor too and then using the square difference expression like this:

Finally, our rational expression can be simplified as:

Therefore, the answers are:
- The numerator is a-2
- The denominator is a+2