In this question, you're plugging in g(x) into f(x) to simplify.
You would plug the g(x) equation into the x variable in the f(x) equation.
Plug g(x) into f(x):
(2x+3)² - 1
Solve:
(2x+3)² - 1
Use FOIL:
F = First
O = Outsides
I = Insides
L = Last
4x² + 12x + 9 - 1
Combine like terms:
4x² + 12x + 8
Answer:
4x² + 12x + 8