A W $1258($A$572$ Grade $50/$A$992$ Steel$)$ Column of $20$ feet length is supported on two ends. Determine the Critical Buckling Load and Critical Stress developed in the Column for the following End Support Conditions. $E=30{10}^3$ksi.

$($a$)$ Both Ends Pinned

$($b$)$ Both Ends Fixed

$($c$)$ One End Free and One End Fixed.