Functions need each input to map to exactly one output. Graphically speaking, this means that any two points on the function cannot have the same x-coordinate.
Given this, the bottom right option is the only one that fits these circumstances.
since you start with 12. 7 and gain .24 each year, you would multiply the years by. 24 and just add the 12. 7 I hope this makes sense. also I love your profile picture :)