PQRS is a trapezium as shown in the figure with PQ ∥ RS, then what is the difference between ∠S and ∠R?

Given: PQ ∥ RS
∠Q = 90°
∠P = 115°
PQ ∥ RS, QR acts as a transversal. Also, ∠Q and ∠R are co-interior angles.
⇒ ∠Q + ∠R = 180° (∵ Sum of co-interior angles is 180°)
⇒ 90° + ∠R = 180°
⇒ ∠R = 90°
In trapezium PQRS, 
⇒ ∠P + ∠Q + ∠R + ∠S = 360° (∵ Sum of all angles of a quadrilateral is 360°)
⇒ 115° + 90° + 90° + ∠S = 360°

⇒ ∠S = 360° - 295°
⇒ ∠S = 65°
Now, ∠R − ∠S = 90° − 65° = 25°
Thus, the difference between ∠R and ∠S is 25°.