input: 0,2.4,8 output: 20,18,16,12

Question

relationship?

Answer 1

Looks like increasing the input by 2 decreases the output by 2.

 

We can think of this as the slope for the relation (line): m = -2/2 = -1

 

The output value is 20 when there is zero input.  We can think of this value as the y-intercept (line).

 

Putting everything together and using y = mx + b for the line, we get y = -x + 20 for the relationship between input (x) and output (y).