A ball thrown up is caught by thrower 6 sec after start. The height to which the ball has risen is (g=10 m/s2)

v = Vi - 10 t

h = Hi + Vi t - 5 t^2
Hi = 0 initial height
t = 6
so t rising = 3 (symmetry of parabola)
v = 0 at top
so
Vi = 10 *t at top = 30 m/s
h = 0 + 30(3) - 5 (9)
= 90 - 45
= 45 meters
(good throw)