Problem $4$

The cable $BC$ exerts an $3$ KN force $F_{BC}$ on the $\frac{?}{\text{b}\text{a}\text{r}}AB$ at $B.$

$($a$)$ Determine the moment $M_A$ of $F_{BC}$ about point $A(0,0,0).$

$($b$)$ Calculate the perpendicular distance $d$ from point $A$ to the cable BC $($line of action of $F_{BC}).$