A circus clown at the top of a 60-foot platform is playing catch with another clown on the ground.

The clown on the platform drops a ball at the same time as the one on the ground tosses a ball upward at 80 ft/sec.

For what length of time is the distance between the balls less than or equal to 10 feet?

Hint: the initial velocity of a ball that is dropped is 0 ft/sec.

The formula for the height S in feet above the earth at a time t seconds for an object projected into the air with an initial velocity of v ft/sec from an initial height of s0 is:

S = -16t2 + v0t + s0