Two parallel lines AB and CD are cut by a transversal PQ at points X and Y respectively, with B and D on the same side of PQ. Angle PXB = 110°.
Find angle XYD.

Angle PXB and angle XYD are corresponding angles (both lie above their parallel line, on the B/D side of the transversal), so angle XYD = angle PXB = 110°. (Check: the co-interior pair angle BXY = 180 - 110 = 70° and angle XYD add to 70 + 110 = 180°.)