Algebra: distance from a fixed point

[drooble122]

Homework Statement

See image

Relevant Equations

Basic algebra

The first image is the question and the second is the answer.
My thinking is let's say North is positive, and South is negative. Fixed point O is the starting point. Then the question becomes +(2a-b)-(3a+2b). The answer should be -a-3b. I cannot fathom why the book gives the answer as a+b. Any help would be appreciated. Thank you.

 

[Doc Al]

I'd say you were correct. What book are you using?

 

[Office_Shredder]

It's probably a typo and they meant to say 2a+b miles north.

 

[Doc Al]

It's probably a typo and they meant to say 2a+b miles north.

Exactly.