Solve the Problem $\mathrm{x}$ , Could Be Approximated by the Polynomial Function

Solve the problem.
-Suppose that the number of frequent flier miles (in billions) earned by customers of various airlines, but not yet redeemed in year $\mathrm{x}$ , could be approximated by the polynomial function:
$$f(x) =0.0017 x^{4}-0.68 x^{3}+11.33 x^{2}-20.15 x \quad(3 \leq x \leq 14)$$
Where $x=0$ corresponds 1980. How many unredeemed miles were there in 1991?

A) About 592 billion
B) About 269 billion
C) About 834 billion
D) About 350 billion