solve only (ii) & explain

solve only (ii) & explain (i) A ray of light incident on face AB of an equilateral glass prism, shows minimum deviation of 300. Calculate the speed of light through the prism. c (ii) ind the angle of incidence at face AB so that the emergent ray grazes along the face AC.

Please find this answer

from snells law,
                         sin i /sin r=µ₁₂ 
for emergent ray to grace through face AC, <r=90^° 
then  at AC, applying snells law, 
                                                   sin i/1=1/sqrt(2)
                                               =>i_AC =45°                  
using snells law,
                       sin i_AB=sin r_AB*µ₁₂                                           [from diagram r_AB=15°]
                        => i_AB=sin^- 1(sin 15)