What's the length of the hypotenuse of the triangle to the nearest tenth

Evaluate the expression for the given value of the variable 2×(c2-5) for c=4

After t seconds, a ball tossed in the air from the ground level reaches a height of h feet given by the equation h = 144t-16t^2. after how many seconds will the ball hit the ground before rebounding?

Can anyone explain to me how to do this? anything will .