Given f(9) = −2, which function can be used to generate the sequence −8, −7.25, −6.5, −5.75,…?

Say f(1) = -8 , f(2) = -7.25, f(3) = -6.5

the difference between fn and fn-1 is 0.75

If we graph each point, we can easily check that the function that describes that sequence is

f(x) = 0.75x - 8.75