Answer
$f(x) = 2(x+5)^2-15$
Work Step by Step
Start by graphing the data and the functions in the same figure window.
$$\begin{aligned}
f(x) &= 1.5(x+5)^2-15 \ ,\ a= 1.5\\
f(x) &= 1.8(x+5)^2-15\ ,\ a= 1.8\\
f(x) &= 2.0(x+5)^2-15\ ,\ a= 2.0\\
f(x) &= 2.3(x+5)^2-15\ ,\ a= 2.3\\
\end{aligned}$$ The graph shows that the parabola that best fit the data is $$f(x) = 2(x+5)^2-15.$$
