$\begin{align}  & \angle ROT=2\times \angle RST=2\times {{49}^{\circ }}\text{    }\!\!\{\!\!\text{ Angle at centre is 2}\times \text{angle subtended at the circumference }\!\!\}\!\!\text{ } \\ & \angle ROT={{98}^{\circ }} \\ & \left| OT \right|=\left| OR \right|\text{    }\!\!\{\!\!\text{ Radius of a circle }\!\!\}\!\!\text{ } \\ & \therefore \angle ORT=\angle RTO\text{     }\!\!\{\!\!\text{ Base angles of an issosceles triangle }\!\!\}\!\!\text{ } \\ & \angle ORT=\angle RTO=x \\ & x+x+{{98}^{\circ }}={{180}^{\circ }}\text{       }\!\!\{\!\!\text{ }\text{Sum of angles in a triangle }\!\!\}\!\!\text{ } \\ & x={{41}^{\circ }} \\ & \angle RTO=\angle STO+\angle RST \\ & {{41}^{\circ }}=\angle STO+{{29}^{\circ }} \\ & \angle STO={{41}^{\circ }}-{{29}^{\circ }}={{12}^{\circ }} \\ & OptionA \\\end{align}$