you could factor this in a few ways, but the easiest is trial and error. check out the products of 63 and see if you can find anything that adds up to -16:
±63, ±1, ±7, ±9... the last two there could work. you know that you'll need two negatives to equal a positive 63, and -7 + -9 = -16, so:
(y - 7)(x - 9) is your factorization.
