Question

What is f(–3) for the function f(a) = –2a2 – 5a + 4?

Answer 1

Its easy 
just substitute (-3) in the place of 'a'.

f(-3) = -2(-3)^2 - 5(-3) +4
        = -18 + 15 + 4
        = 1

I hope this helped :D

Answer 2

F(-3) = -2(-3)2 - 5(-3) +4
            - 6 x 2 -15 + 4
                - 12 -15 +4
                    - 27 + 4
                           -23

I believe this is how to solve the equation. I could be wrong.