A is the linear function.
Explanation
You find the slope by taking sets of 2 points at a time and use the slope formula of change in y divided by change in x.
In every case , this -3 is the same slope so it is a linear line.
You could go farther but it is not required. The equation is y = -3x + 18. You determine the y= Mx+b by plugging the slope into the m and any two of your given points.
Hope this helps and you have a great day.
