ABCD is an isosceles trapezium as shown in the figure, in which $$AB = DC$$, $$\angle DAP = 20^\circ$$, DP is perpendicular to AP, $$\angle C = 70^\circ$$, QR is the bisector of $$\angle BQD$$ and $$PS \perp QR$$. Calculate $$\angle SPQ$$ and $$\angle SRA$$. Justify each of the steps in calculation.