Derivative of position-time gives velocity-time. Derivative of velocity-time gives acceleration.

Well, we know the acceleration.

So now if we take the integral of acceleration, we get velocity.

And we know that at 0 seconds, we're traveling -20ft/s

And so we get:

The integral of this will then give us distance:

And we know that we are 245 feet up at 0 seconds.

And thus our final equation:

You may recognize this last equation from physics class.

d = (vi)t + 1/2at^2

In the form of d - 245