if a ball is thrown vertically upward at 30 m/s, then its approxiamte height im meters t seconds later is given by

h(t)=30t-5t^2

1) what is the domain of h?

2) for what time limit is theball more than 45 feet above the ground?

3) Whatis themaximu height of the ball?

4) After how many seconds does the ball reach the maximun height?

please please help.