(b) Change a quadratic equation to vertex form by completing the square:
The vertex is (5, 65), and this is the maximum point of the parabola. So the greatest height is 65 feet.
(c) Since the projectile started at t = 0 from the top of the building, plug in 0 for t into the equation and simplify.
(d) When the projectile hits the ground, h = 0. So plug in 0 for h into the equation and solve for t.