$(4)$ Replace the three forces acting on the frame by a resultant force and a resultant moment at point $B.$ Use the geometric method to determine the moment about $B,$ and point $D$ is the midpoint of bar $AB.$

Ans: vec$(R)=12$vec$(i)+8$vec$(j)-16$vec$(k)$ kips,

vec$(M{)}_B=80$vec$(i)+84$vec$(j)+72$vec$(k)$ kip$-$ hat$(t)$