b
\(\,\,\frac{{sin\,60}}{{sin {r_1}}}\,\, = \,\,\sqrt 3 \,\,\, \Rightarrow \,\,\sin \,{r_1} = \,\,\frac{{\sin \,60}}{{\sqrt 3 }}\)

\(\sin \,{r_1} = \,\,\frac{{\sqrt 3 }}{2}\,\, \times \,\,\frac{1}{{\sqrt 3 }}\,\, = \,\,\frac{1}{2}\,\,\, \Rightarrow \,\,\,{r_1} = \,\,{30^ \circ }\)

હવે, \(sin\,({i_1} - {r_1})\,\, = \,\,\frac{d}{5}\,\) અથવા  \(d\,\, = \,\,5\,\,sin\,\,({i_1} - {r_1})\,\, = \,\,\frac{5}{2}\,\,cm\)