a.
In order to calculate the angle of refraction, we can use the law of refraction below:

Where n1 and n2 are the index of refraction and theta1 and theta2 are the incident and refracted angles.
So, using n1 = 1.33, theta1 = 15° and n2 = 2.42, we have:

b.
To calculate the velocity of light in diamond, we can use the formula below:
