Answer
$f(x) = -1.4(x-3)^2+9$
Work Step by Step
Start by graphing the data and the functions in the same figure window.
$$\begin{aligned}
f(x) &= -1.3(x-3)^2+9 \ ,\ a= -1.3\\
f(x) &= -1.4(x-3)^2+9 \ ,\ a= -1.4\\
f(x) &= -1.5(x-3)^2+9 \ ,\ a= -1.5\\
f(x) &= -1.6(x-3)^2+9 \ ,\ a= -1.6\\
\end{aligned}$$ The graph shows that the parabola that best fit the data is $$f(x) = -1.4(x-3)^2+9.$$
