As $\mathrm{PQRST}$ is a regular pentagon, each of its internal angles is ${108}^{\circ }$. The internal angles of the quadrilateral $\mathrm{PRST}$ add up to ${360}^{\circ }$ and so by symmetry $\angle \mathrm{PRS}=\angle \mathrm{RPT}=\frac{1}{2}({360}^{\circ }-2\times {108}^{\circ })={72}^{\circ }$. Each interior angle of a regular hexagon is ${120}^{\circ }$, so $\angle \mathrm{PRU}={120}^{\circ }$.

Therefore $\angle \mathrm{SRU}=\angle \mathrm{PRU}-\angle \mathrm{PRS}={120}^{\circ }-{72}^{\circ }={48}^{\circ }$.