Really hard math problem!!?

A launched rocket has an altitude, in meters, given by the polynomial h + vt - 4.9t^2, where h is the height, in meters, from which the launch occurs, at velocity v in meters per second, and t is the number of seconds for which the rocket is airborne. If a rocket is launched from the top of a tower 70 meters high with an initial upward speed of 20 meters per second, what will its height be after 3 seconds?