I just had a lightbulb moment. So the direction needs to be up and to the left, as in the upper right side of the diagram you showed me. So the third wire has to be down and to the left of point P.
My next question is if it has to be down and to the left of point P, how far from point P...
If 3,5 produces an upward-rightward direction of B at 8,0 where else should the third wire be?
I think it has to be to the right of point P to get the upward-leftward B to counteract from the first two wires but I'm not sure if I'm on the right track or not.