$10\mathrm{.}58$ A W$831-$rolled$-$steel shape is used for a column of $21-$ft effective length. Using allowable stress design, determine the allowable centric load if the yield strength of the grade of steel used is $($a$){}_Y=36$ksi, $($b$){}_Y=50$ksi. Use $E=29{10}^6$psi