A ball is projected vertically upward from the ground. It passes a point 25m above the ground twice, the two instants being 4s apart. Ignoring air resistance and taking g=9.8m s−2 downward, the initial speed of projection is
(a) 22.1m s−1
(b) 30.0m s−1
(c) 29.6m s−1
(d) 25.8m s−1