f(x) = -5.
This function is independent of x. There is no term associated with x on the function.
Therefore f(8.6) = -5 still.
f(8.6) = -5.
From the options there is no answer.
OR
you can write f(x) = -5
f(x) = -5x⁰ because x⁰ = 1.
f(8.6) = -5*8.6⁰ = -5 *1, 8.6⁰ = 1
(Any non zero raised to power zero is 1)
f(8.6) = -5
NO ANSWER from the options given.