How to find r subscript n in this vector problem

[ohheytai]

i uploaded it i can't figure out r subscript n i have no idea can someone help me its my last try thanks

 

[0ddbio]

It says that $r_{n}$ and $r_{a}$ give the position with respect to the origin, while r is a relative position vector.

So what vectors would $r_{n}$ and $r_{a}$ be if they start at the origin? Where would the end of those vectors lie? Given that $r = r_{n} - r_{a}$.
If the answer isn't obvious then review material on graphically subtracting vectors.

 

[ohheytai]

i only have the vector sum though and i don't have those two vectors

 

[cupid.callin]

Note that in a displacement vector r = ra - rb

ra is the vector from origin to head of the vector r
and rb is vector from origin to tail of vector r