Let's presume a number as 10x + y where x is a second digit and the y is the first. Say, 54 can be presented as x equal to 5 and y equal to 4.
So, any "imagined" number would be:
(10x + y) - (x + y)... that is
10x + x + y - y = 9x.
That means all the answers are devided by 9 without remeinder. Let's now attentively look at the picture: all the numbers that are devided by 9 are alike:
This is a trap.