The $60-$kg ventilation door $\backslash ($ O D $\backslash )$ with mass center at $\backslash ($ G $\backslash )$ is held in the open position shown by means of a moment $\backslash ($ M $\backslash )$ applied at $\backslash ($ A $\backslash )$ to the opening linkage. Member $\backslash ($ A B $\backslash )$ is parallel to the door for the $\backslash (21^\{\backslash$circ$\}\backslash )$ position shown. Determine the magnitude of the moment $\backslash ($ M $\backslash ).$

Answer: $\backslash ($ M$=\backslash )\backslash (\backslash$mathrm$\{$N$\}\backslash$cdot $\backslash$mathrm$\{$m$\}\backslash )$