A cylindrical water tank 0.6 m in diameter has its axis vertical and is to be provided with an…

A cylindrical water tank 0.6 m in diameter has its axis
vertical and is to be provided with an orifice at its bottom. If the Cd
of the orifice is 0.65, what size of orifice is needed to lower the water
surface elevation, measured above the base of the tank, from 1.5 m to 0.8 m in
30 s?