hi

[rich lava]

f is a function taking x as an input. In this question, for any given x you choose to pass through f, it returns f(x), which in this case is 3(x^2) + 9x - 12. This holds for whatever value of x you input. To find f(n), (where n is any number you want) simply replace x with it and simplify

[heavy edge]

ah okay thank you so so much!

[idle field]

@heavy edge has given 1 rep to @rich lava