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!
1st point: ( -5+8. 1-2 ) = ( 3, -1 )
2nd point: ( -3+8, 7-2 ) = ( 5, 5 )
Answer: C) translation right 8 units and down 2 units.