Answer:
a. The refractive index ranges from 1.5 - 1.56
b. 18.7° for violet light and 19.5° for red light.
c. 33.7° for violet light and 35.3° for red light.
Explanation:
a. The refractive index of an object is the ratio of the speed of light in a vacuum and the speed of light in the object.
Mathematically,

The speed of violet light in the object is
.
The speed of red light in the object is 
Hence, the refractive index for violet light is:

and for red light, it is:

Hence, the refractive index ranges from 1.5 - 1.56.
b. The refractive index is also the ratio of the sine of the angle of incidence to the sine of the angle of refraction.

The angle of incidence is 30°.
The angle of refraction for violet light will be:

And the angle of refraction for red light will be:

The angle of refraction for red light is larger than that of violet light when the angle of incidence is 30°.
c. The angle of incidence is 60°.
The angle of refraction for violet light will be:

And the angle of refraction for red light will be:

The angle of refraction for red light is still larger than that of violet light when the angle of incidence is 60°.