Answer 4a and 4b please

4a (6pts). Find the critical angle of ray of light at glass-water interface if refractive indices for glass and water are 1.54 and 1.33 respectively. 4b-(11 pts). An object is located 14.0 cm in front of a convex mirror, the image being 7.00 cm behind the mirror. A second object , twice as tall as the first one, is placed in front of the mirror, but at a different location. The image of this second object has the same height as the other image. How far in front of the mirror is the second object located