Question

Gandalf the Grey started in the Forest of Mirkwood at a point with coordinates (1, -3) and arrived in the Iron Hills at the point with coordinates (2, 1). If he began walking in the direction of the vector v = 3 I + 1 J and changes direction only once, when he turns at a right angle, what are the coordinates of the point where he makes the turn.

( ??? , ??? )