d
(d) From figure it is clear that \(\angle \,e = \angle \,{r_2} = 0\)

From \(A = {r_1} + {r_2}\)\( \Rightarrow {r_1} = A = {45^o}\)

\(\therefore \mu = \frac{{\sin i}}{{\sin {r_1}}} = \frac{{\sin 60}}{{\sin 45}} = \sqrt {\frac{3}{2}} \)

Also from \(i + e = A + \delta \)

\( \Rightarrow 60 + 0 = 45 + \delta \)

\( \Rightarrow \delta = {15^o}\)