$(3)$ A downward $6001$ lb force and a counterclockwise moment $M$ are applied to the three$-$bar frame as shown. Determine $($a$)$ the moment $M$ applied at pin $A$ to keep the loaded frame in equilibrium, $($b$)$ the magnitude of the reaction at the pinned support $B.$

Ans: $($a$)M=1350lb-$ft $($b$)B=984lb$