Question 717771
All you know is that
(1) q(x)*f(x) = 1
When you are given that 
(2) q(2) = 10 you can use (1) to find
(3) f(2) = 1/10
But since you don't know the functions q(x) or f(x), you have no way to evaluate f(4).
The answer to,"What is f(4)", is
(4) f(4) = 1/q(4)