Chapter 6.3, Problem 4P

For Problems 2 to 6, given $A=i+j-2k,B=2i-j+3k,C=j-5k$:

Let $O$ be the tail of $B$ and let $A$ be a force acting at the head of $B$.

Find the torque of $A$ about O ; about a line through $O$ perpendicular to the plane of $A$ and $B;$ about a line through $O$ parallel to $C$.