I think I can give you the answer, but I don't think I can explain it very well.
It looks like you are starting out at 2 and progressing to 3. The problem is that the answer has a minus sign after the two.
What I am assuming is that you know what a minus number is and what you do when 2 of them are in a row. If you do, then you should write
2 - -1 = 3
The first box contains -1 and the second box contains 3.
