If a baseball player hits a baseball from 4 feet off the ground with an initial velocity of 64 feet per second, how long will it take the baseball to hit the ground? use the equation h=-16t^2+64t+4.

Right now that equation is a function of time, h(t), height with respect to time.  If the baseball is on the ground, it has no height.  In other words, its height = 0.  So if we set the equation equal to 0 and solve for t, time, that will tell us the time that the ball had a height of 0.  If you plug those numbers into the quadratic formula, which is the best and most efficient way to factor a quadratic, you will get that the times are -.0615528128 and 4.061552813 seconds.  The 2 things in math that will never EVER be negative are time and distance/length.  So we know that the ball will not hit the ground at -.062 seconds.  Therefore, it hits the ground 4.06 seconds after it was hit.