What is the value of the function?
f(-2)

Since, the function equation is given by the model: f(x) - I'm adapting it to your question...In saying so, in order to find norminal or in-norminal values, we need to substitute the value of 'x' into the equation.
In your case, f(-2). Following the model f(x), the x = -2. You can't do much with your question, but with the rest of the equation, it will come handy.
For example, say x = -2
Substitute into equation;
thus, 
f(-2) = a(-2)² + b(-2) + c Or however it's shown. 

I hope this makes sense :) Just keep in mind of formulas and rules. It should guide you through. :) 

Well, we don't exactly know what the function is, but simply substitute -2 for any x