math,help

The height h in feet of an object after "t" seconds is given by the function

h = -16t^2+70t+8

How long will it take the object to hit the ground? round answer to nearest thousandth

this is what i have

-16t^2+70t+8=0

x = (-70 +/- sqrt (4388))/(-32)

from this point on i have no idea i used the quadratic equation

Well you are on the right track, only your equation should look like
(-70 +/- sqrt(5412)/(-32) because in your quadric equation it's -4ac, and a is -16 so the double neg makes it positive, so you have to ad it to 70^2. From there just solve it out for x. Do -70 minus sqrt(5412)/(-32) and
-70 plus (5412)/(-32). you will get two answers, and the negative one is the wrong one. Hope this helps :)

this is what i get:
2.2989467 and if i round to the thousandths.
2.3

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