Assuming that we are talking about Earth's atmosphere (and which a = -9.8) and s = 0, this becomes:
s(t) = -4.9t^2 + 17t.
From here, part a) can be solved by finding the y-coordinate of the
vertex, part b) can be solved by finding the x-coordinate of the vertex,
the answer to part c) is the same to that as part b) as it takes the
same amount of time for it to fall back down, and part d) can be solved
by differentiating and finding the slope of the tangent line at the
point the ball hits the ground.