In the interior of a cylindrical tank, water flows through a tube 1 with a velocity v1 = 20 m / s and leaves through tubes 2 and 3 with velocities v2 = 8 m/s and v3 = 10 m/s respectively. At 4 there is a vent valve open to atmospheric air. (a) What is the speed with which the water level falls in the tank?
(b) what is the average speed of the air flow in valve 4? assuming air is incompressible.

Assume the following pipe diameters: D1 = 3 m, D2 = 2 m, D3 = 2.5 m, D4 = 2 m