### Home > GC > Chapter 12 > Lesson 12.2.4 > Problem 12-87

Perry threw a tennis ball up into the air from the edge of a cliff. The height of the ball was

*y*= −16*xs*^{2}+ 64*x*+ 80 , where*y*represents the height in feet of the ball above ground at the bottom of the cliff, and*x*represents the time in seconds after the ball is thrown. Homework Help ✎How high was the ball when it was thrown? How do you know?

What was the height of the ball 3 seconds after it was thrown? What was its height

a second after it was thrown? Show all work. When did the ball hit the ground? Write and solve an equation that represents this situation.

Substitute 0 in for *x*.

*y* = -16(0²) + 64(0) + 80 = 80 feet

Substitute 3 for *x* in the given equation.

*y* = -16(3²) + 64(3) + 80*y* = -144 + 192 + 80*y* = -144 + 272*y* = 128 ft

*y* = -16(0.5²) + 64(0.5) + 80*y* = -4 + 32 + 80*y* = -4 + 112*y* = 108 ft

If the ball hits the ground, what is its height above the ground?

-16*x*² + 64*x* + 80 = 0

−16(*x*² − 4*x* − 5)

−16(*x* − 5)(*x* + 1)*x* = 5 seconds