$3)$ A wheat process roller mill operates with a multi$-$plate disc chitch system having inner radius of $100$mm and is $(1)/(2)$ times the extemal radius. Available information shows that $70$kw of power was transmitted at a rotational speed of $1200$ revolutions per minutes, the allowable pressure intensity and coefficient of friction are $140$kN $/$ m $*$ r $^2$ and $0\mathrm{.}03$ successively. Determine $(1)$ The external radius of the clutch $($ii$)$ Axial force on the clutch $($iii$)$ Effective mean radius $($iv$)$ Number of plates needed to transmit the torque $($v$)$ The torque.