I think the rule has something to do with adding. I noticed that when the input was at 0 the output was 20, When the input was 15 the output was 5, when the input was 8 the output was 12, and so on. I think the rule is, no matter what number is in the input or the output, it must equal 20.
Hope This Helps!
Look up math way and type it in its free and it will help alot.
We need the figure to answer that.
