-- It'll be a lot easier if you clean up the function first.
You're not changing the function. You're just making it
easier to read and work on without mistakes.
Notice that 3x3=9 , so the function is f(x) = 9 - 4x + 5
Combine like terms, and the function is f(x) = 14 - 4x .
Much easier to work with.
-- Now, when somebody tells you to evaluate the function for some number,
just take their number, write it in place of 'x',and see what you've got.
Example:
f(x) = 14 - 4x
Evaluate f(x) for x = 3.
-- Write 3 in place of 'x' in the function: f(3) = 14 - 4(3)
-- 4(3) = 12 . So the function is f(3) = 14 - 12
-- Finish up the subtraction : f(3) = 2
You just evaluated f(x) for x=3.
Nice job !