Since the distance varies directly as the square of time, then its expression looks like this:

Where d is the distance, "k" is the proportionality constant and t is the time the object is falling. We know that after 6 seconds the stone travels 304 feet. With this information we can determine the value of "k".

Therefore the complete expression is:

We want to know the distance after 7 seconds, therefore t = 7.

The stone will travell approximatelly 314 feet in 7 seconds.