$"6\mathrm{.}84$ Solve Prob. $6\mathrm{.}83,$ assuming that a $6-$mm$-$thick plate is bent to

form the channel shown. $*6\mathrm{.}83$ A steel plate, $160mm$ wide and $8mm$ thick, is bent to form the

channel shown. Knowing that the vertical load $P$ acts at a point

in the midplane of the web of the channel, determine $($a$)$ the

torque $T$ that would cause the channel to twist in the same way

that it does under the load $P,(b)$ the maximum shearing stress

in the channel caused by the load $P.$

Fig. P$6\mathrm{.}83$