$8\mathrm{.}120$ A cable is placed around three parallel pipes. Knowing that

the coefficients of friction are s $=0\mathrm{.}25$ and k $=0\mathrm{.}20,$ determine

$($a$)$the smallest weight W for which equilibrium is maintained, $($b$)$ the

largest weight W that can be raised if pipe B is slowly rotated counterclockwise while pipes A and C remain fixed.