Replace x with the binomial a - 2.
f(a - 2) = [3(a - 2) + 5]/(a- 2)
f(a - 2) = [3a - 6 + 5]/(a - 2)
f(a - 2) = [3a - 1]/(a - 2)
f(a - 2) = (3a - 1)/(a - 2)
Done.
