You kick a ball off the ground with a horizontal speed of 16 m/sec and a vertical speed of 20.7 m/sec.
1. The ball reaches it's highest point how many seconds after it is kicked.
2. It reaches the ground how many seconds after it is kicked.
the height is
h(t) = 20.7t - 4.9t^2
That's just a parabola; the max height is at the vertex.
Now just solve for t when h=0.
To save yourself some work, the max height is reached at the center of its flight, so you really only need to calculate one of the above answers, then the other is obvious.