A ball is thrown downward from the top of a 240-foot building with an initial velocity of 20 feet per second. The height of the ball h in feet after t seconds is given by the equation h= -16t^2 - 20t + 240. How long after the ball is thrown will it strike the ground?

3.29 s

Step-by-step explanation:

We are given that

Height of building=240

Initial velocity=20ft/s

The height of the ball  after t seconds is given by

When the ball strike the ground then

h(t)=0

Quadratic formula:

Using the quadratic formula

Time cannot be negative .Therefore,

t=3.29 s

the solution is h=10 because you add 9 to each side of the equation.