160441

Let's say the number were to be xy (the value being 10x+y). It then says to add together the digits (x+y) and take that away from your original number; this leaves you with 9x. This means that, whichever the first digit of your number was, the answer will be 9 times of that-it will have to be a multiple of 10. On the chart, all of the multiples of 9 are the same symbol (but they change each time you retry the puzzle) so it cannot be anything except that symbol.