A ball is thrown vertically upward from the edge of a balcony 20m above the ground with a speed of 15m s−1. It rises, returns past the balcony and strikes the ground below. Neglect air resistance and take g=9.8m s−2 downward. The speed with which it hits the ground is closest to
(a) 19.8m s−1
(b) 24.8m s−1
(c) 29.8m s−1
(d) 15m s−1