[tex]\angle R[/tex] and [tex]\angle S[/tex] are supplementary by the same-side interior angles theorem, and [tex]\angle S \cong \angle T[/tex] because of the properties of an isosceles trapezoid, meaning that [tex]\angle R[/tex] and [tex]\angle T[/tex] are supplementary.
[tex]4x+11+2x-5=180\\\\6x+6=180\\\\6x=174\\\\x=\boxed{29}\\\\\implies m\angle S=m\angle T=2(29)-5=\boxed{53^{\circ}}[/tex]
