You're in luck.
When faced with a monster like this, take some time to look it over.
Notice that the first term is a square, the last term is a square, and
the middle term is double the product of the square roots. Noticing
this, you realize immediately that the whole thing is a perfect square,
and you can write its equivalent by inspection:
49p² -84pq + 36q² = (7p - 6q)²