I need help this is for homework this problem but i feel like i can't solve because i am missing some information or am i wrong. If so what am i suppost to do...help me

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 the nearest thousandsth.

The ground is at h=0. That is the information you need.

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

solve for t. Notice it is a quadratic, and has two solutions. In this case, ignore the negative solution (you can think out why).