Answer:
270°
Step-by-step explanation:
∠ PQR = 90° ( angle in a semicircle )
PRST is a cyclic quadrilateral
The opposite angles in a cyclic quadrilateral are supplementary, sum to 180°
Then
∠ PRS + ∠ PTS = 180°
∠ PQR + ∠ PRS + ∠ PTS = 90° + 180° = 270°
