A firecracker shoots up from a hill 145 feet high, with an initial speed of 80 feet per second. Using the formula H (t) = - 16t2 + vt + s, approximately how long will it take the firecracker to hit the ground?

13 seconds

11 seconds

Nine seconds

Six seconds

Plugging in the given values gives us:

0 = - 16t^2 + 80t + 145

This a quadratic equation with two roots. Solving it using using the quadratic formula or by factoring, or by any other solution, the roots are:

6.4531 and - 1.4131

We are dealing with time, so we choose the positive root.

Therefore, the answer is 6.4531 seconds