Water $(\rho = 1000 \: kg/m^3)$ flows through a venturimeter with inlet diameter $80 \: mm$ and throat diameter $40 \: mm$. The inlet and throat gauge pressures are measured to be $400 \: kPa$ and $130 \: kPa$ respectively. Assuming the venturimeter to be horizontal and neglecting friction, the inlet velocity (in $m/s$) is _______