Answer:
Maybe -3
Explanation:
I am not 100% sure but it is better than nothing,
since 3+3=6 I think after 3 is 6, and after 6 is 9. I think that because the more right the line goes you add 3 to every move. So therefore, 3-3=0, and 0-3= -3
Hope this helps. Also, I hope I gave you the correct answer.