make sure you give AL2006 a medal
First of all, as you read the problem, it should begin to dawn on you that
you'll need to know their greatest common factor. So let's find that:
The factors of 56 are 1, 2, 4, 7, 8, 13, 28, and 56 .
The factors of 64 are 1, 2, 4, 8, 16, 32, and 64 .
The common factors of 56 and 64 are 1, 2, 4, and 8 .
The greatest one is 8 .
56 = 8 x 7
64 = 8 x 8
So the sum of (56 + 64) is the sum of (8 x 7) + (8 x 8).
You can 'factor' 8 out of the terms of that sum, and get
56 + 64 = 8 x (7 + 8) <== that's the answer