Answer
$f(x) =-2(x-7)^2+15$
Work Step by Step
$$\begin{aligned}
f(x) &= 2(x-7)^2+15 \ ,\ a= 2
\end{aligned}$$ The best eyeball fit to the data can be found by setting the constant $a= -2 $. Hence, we have $f(x) =-2(x-7)^2+15 $ as the best eyeball fit to the data.
