Question

what is the formula if the inputs are 15,16,17,and 18 and the output is 2,4,6,and 8?

Answer 1

call the inputs x and the outputs y.

Each time x increases by 1, y increases by 2.

So, y = 2x + ...
Since x starts at 15, but y starts at 2*1, we can say

y = 2(x-14) = 2x - 28

Answer 2

Steve, that was very clever!