The planar structure RST shown in the figure is roller-supported at S and pin-supported at R. Members RS and ST have uniform flexural rigidity (EI) and S is a rigid joint. Consider only bending deformation and neglect effects of self-weight and axial stiffening.When the structure is subjected to a concentrated horizontal load P at the end T, the magnitude of rotation at the support R, is

• A. \(\frac{{P{L^3}}}{{12EI}}\)
• B. \(\frac{{P{L^2}}}{{12EI}}\)
• C. \(\frac{{P{L^2}}}{{6EI}}\)
• D. \(\frac{{PL}}{{6EI}}\)