A$)$ A light triangular plate OAB is in a horizontal plane. Three forces, $F_1=6\mathrm{.}0N,F_2=9\mathrm{.}0N,$ and $F_3=7\mathrm{.}0N,$ act on the plate, which is pivoted about a vertical axes through point $O.$ In the figure, vec$(F{)}_2$ is perpendicular to $OB.$ Find the net torque about the vertical axis through point $O,$ acting on the plate due to forces $F_1,F_2,$ and $F_3.$

Figure $8$