Given the function f(t)= -16t^2+24tHow high the ball is above the ground after how many seconds?

Since the function f describes the height of the ball as a function of time, then, the ball is f(t) feet above the ground after t seconds.
Since f(1) = 8, this means that the ball is 8 feet above the ground after 1 second.
Therefore, the answers are:
The ball is 8 feet above the ground after 1 seconds.