answer:the radius r = 30 cm
the formula of a circumference of a circle:
r - radius
h(t) = 144·t - 16·t^2 = 16·t·(9 - t) = 0
9 - t = 0 --> t = 9
the ball will hit the ground after 9 seconds.
the quadratic formula is , where a, b, and c are values in the quadratic ax^2 + bx + c. plug in the values to get