Question

if PQ||st, <PQR =110 and <RST=130,find <QRS

Answer 1

Draw a line parallel to both the given lines from point R. Let XRY be the name of line.
∠SRY + 130° = 180° (co interior angles)
∠SRY = 50°

Similarly ∠QRX = 70°

Now XRY is a straight line 
⇒∠QRX + ∠SRY + ∠QRS = 180°
⇒∠QRS = 180° - 120° = 60°