160089

First I looked at a few of the outcomes of the machine.
I then found that they were all multiples of nine.
So I then looked back at the equation on the board and thought how I could represent each digit of the number in my equation.
I then realized that you could represent each digit separately;
So I put each number as 10a plus b;
Then take a plus b and you get the multiple of nine;
I then simplified by ignoring the b because we add b then take b so we don't need to put it in in the first place and taking the a out and then taking the 10a down too 9a
Which got me to my final equation (9a);

(10a+b) - (a+b)
(9a)