$($b$)$ In a multi plate clutch radial width of the friction material is to be $0\mathrm{.}2$ of maximum radius. The coefficient of friction is $0\mathrm{.}25.$ The clutch provides $60$ kW at $3000$ rpm $.$ Its maximum diameter is $250$ mm and the axial force is limited is to $600$ N $.$ Determine ;

$($i$)$ Number of driving and driven plates

$($ii$)$ Mean unit pressure on each contact surface assume uniform wear.

$3+7=10$