Question 69375
You are given the expression:

f(x) = 2x - 1

The notation f(-9) simply tells you that you substitute -9 for x in the expression

f(x) = 2x-1

In this case the substitution of -9 for x leads to:

f(-9) = 2(-9) - 1 = -18 - 1 = -19

so f(-9) = -19