-3pa - 9b - 18pc
For starters, you know that you can't take away any of the letters from the equation because none of the three have the exact same letter; however, they all have something they can be divided by and that is -3.
It would be -3 instead of just 3 because the equation itself starts with a negative. (you could probably do it anyways with just 3, but you'd end up taking out a negative one, anyways, so what's the point?)
Now, you would have: -3 ( pa + 3b + 6pc )
That is truly all you can take out. So, that would end up being your answer since all you can really do is simplify.