How do you get the sum of the numbers 56 and 64 as the product of their greatest common factor and another sum

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