$(3)$ The uniform rectangular plate is

supported by two hinges at A and B and held

in the horizontal position by cable EF as

shown. The weight of the plate is $750$ lb and

a $300$ lb force is applied at corner D of the

plate. Determine $($a$)$ the tension T in cable

EF$,($b$)$ the magnitude of the reaction force

normal to the hinge axis at hinge B$.$

Ans: $($a$)$ T$=495$lb $($b$)$ B$\_($n$)=304$lb