Yacht A's departure position is (50, 20). When it catches up with A, the position of yacht A is (110,20).

The walking distance of ∴A is 1 10-50=60.

∵B's speed is 1.5 times that of A.

∴B is gone, 1.5*60=90.

∴B's departure position is110-90 = 20 (20,20).