I am having difficulty with functions. Not understanding how to solve, how to determine the number that goes for x. here's the question, please help if you can:

f(x) = 3x(2x - 1). f(-1) =

1. I don't understand why the period (.) is there.
2. I substituted -1 for x but could not come up with an answer that was available out of my 4 choices.

a. 7
b. 11
c. -6
d. 9

please help and explain the process.
thanks

you sub in -1 for all x values in the equation.

3(-1) (2(-1) -1) start by subbing in -1 for all of the x values in the equation..
-3 (-2 - 1) multiply 3 and 2 by -1.
-3 (-3) following the order of operations, you do what is in the parentheses first.
9 multiply -3 by -3, and you get 9.