I) The same force (1.2 kgf) would be exerted at the bottom of the bottle, as the force exerted in a fluid gets transmitted undiminished in all directions.
returns after 6 seconds
If the ball returns after 6 s, then the time taken by it to reach the height is 6/2= 3s
first eq of motion, v=u+gt
0=u+(-10)*3 (here, g=-10 m/s^2 as the ball is thrown against gravity)
u=30m/s (initial velo)
Now using third eq
0=(30)^2+ 2 (-10)s