Question 660300
Let x and y be the two numbers.  There are two cases: (1) we subtract y from x to get the difference (y is the minuend and x is the subtrahend), and (2) we subtract x from y to get the difference (x is the minuend and y is the subtrahend).

In the first case:
n = (x+y) - (x-y)
n = x + y - x + y
n = 2y

In the second case:
n = (x+y) - (y-x)
n = x + y - y + x
n = 2x

So we can say that the answer is twice the the number we choose for the subtrahend when we find the difference of the two numbers.