Answer:
You can rightly guess that ballistic motion is described by a quadratic function.
Differences of the y-values are 5.75, 3.25, 0.75, -1.75, -4.25.
First differences are not constant but form a linear sequence that decreases by 2.5 between each pair. Since second differences are constant, the function is described by a 2nd-degree polynomial function, a quadratic.