Can someone help me? Will medal and fan!

A firecracker shoots up from a hill 160 feet high, with an initial speed of 90 feet per second. Using the formula H(t) = −16t2 + vt + s, approximately how long will it take the firecracker to hit the ground?

Five seconds
Six seconds
Seven seconds
Eight seconds

Question

Can someone help me? Will medal and fan!

A firecracker shoots up from a hill 160 feet high, with an initial speed of 90 feet per second. Using the formula H(t) = −16t2 + vt + s, approximately how long will it take the firecracker to hit the ground?

 Five seconds
 Six seconds
 Seven seconds
 Eight seconds

anonymous · Answer

Seven Seconds

anonymous · Answer

Thank you, but can you also explain it, please?

anonymous · Answer

16t^2 - 90t-160 = 0
solving for t:
t = 7 secs approx.