\(\therefore \,\,R \propto {u^2}\sin 2\theta \)
\(\frac{{{R_2}}}{{{R_1}}} = {\left( {\frac{{{u_2}}}{{{u_1}}}} \right)^2}\,\,\left( {\frac{{\sin \,2{\theta _2}}}{{\sin \,2{\theta _1}}}} \right)\)
\( \Rightarrow {R_2} = {R_1}\,{\left( {\frac{{2u}}{u}} \right)^2}\left( {\frac{{\sin {{90}^o}}}{{\sin {{30}^o}}}} \right) \)
\(R_2 = 8{R_1}\)