Answer:
Step-by-step explanation:
h is the height of the pebble after a certain amount of time has gone by. Since we are told to find that time when the pebble is on the ground, we say that h = 0 since the height of something on the ground has no height at all. Then factor the quadratic.
Throw that into the quadratic formula or however you were taught to factor irrational quadratics (maybe completing the square?) to get that
t = 11.27869 sec and t = -10.52869 sec
Since we all know that time will never carry a negative value, we will disregard it and go with 11.27869 seconds. Not sure to where you are told to round.