Answer:
We have the following function:

And this function models the height
, in feet, of an object above ground
seconds after being launched straight up in the air. The graph of this function is shown below. So we want to know what the number 72 represents. Well, what if
?
If
we have:

Thus, 72 is the height of the object above the ground at
. In other words, 72 is the initial height of the ball before being launched straight up in the air.