$4-2.[20$ points$]$ In the unloaded configuration of the mechanism shown, the weight of

the boom and hanging chair induces a compressive force of $575$ N in hydraulic cylinder

$AB.($Compressive means that the force which cylinder $AB$ exerts on point $B$ is directed

from A toward $B.)$ If $=71$ and the length of cylinder $AB$ is $1212$ mm $,$ determine the

moments of this cylinder force acting on pin $B$ about $($a$)$ point $O$ and $($b$)$ point $C.$ Note:

figure dimensions are in millimeters.