160007

The machine knows the number because no matter what number you choose, the end result will be a multiple of 9. So the machine fills all the multiples of 9 with the same emoji. It is a multiple of 9 because assuming that the number you chose is N. N=10A+B where A is equal to the digit in the tens place and B is equal to the number in the units place. A+B=C. N-C=?. Using the substitution method, that means N-C=(10A+B)-(A+B)=9A. So since the answer is 9A, it’s a multiple of 9.