A$]$ Water flowst through a horizontal pipe $1\mathrm{.}0$ m diameter. Aventuri$-$meter of throat diameter $0\mathrm{.}5$ m is fitted to the pipe to measure the discharge. If the reading of the differential head manometer filled with mercury is $20$ cm $.$

A$-1]$ Calculate the flowing discharge in the pipe.

A$-2]$ If the venturi$-$ meter is replaced by orifice meter and a specification plate on the side of the meter reads $"C_v=0\mathrm{.}605"$ For the same discharge, the attached mercury$-$water manometer registers a pressure difference of $9\mathrm{.}5$ cm $.$ What is the size of the orifice meter?