The top of a water tank is open to air and its water level is maintained. It is giving out 0.74 m3 water per minute through a circular opening of 2 cm radius in its wall. The depth of the centre of the opening from the level of water in the tank is close to:
a. 6.0 m
b. 4.8 m
c. 9.6 m
d. 2.9 m