Hello Spandana,

Use the princple of Continuity, i.e. A*V=constant, i.e. product of  Area of Cross section of tube and velocity with which liquid flows is constant.

Applying relation A*V=A'*V', where A,V are initial area and velocity, and A',V' are final area and velocity respectively, you should get

velocity as 12m/s

Hope this Helps

Regards