As PQRST is a regular pentagon, each of its internal angles is 108^°. The internal angles of the quadrilateral PRST add up to 360^° and so by symmetry

ÐPRS=ÐRPT=

1 2

(360°-2×108 °)=72°

. Each interior angle of a regular hexagon is 120^°, so ÐPRU=120^°.

Therefore ÐSRU=ÐPRU-ÐPRS=120^°-72^°=48^°.