The law of refraction as a straight line

A student shone a ray into a plastic block at six angles and measured the angle of refraction each time. You will make the program find $\dfrac{\sin i}{\sin r}$ for each reading and the average, which is the refractive index of the plastic. Then it draws $\sin i$ against $\sin r$: a straight line whose slope is $n$.

Your tasks.

1. Inside the loop, work out ratio, $\dfrac{\sin i}{\sin r}$ for one reading.
2. Find n_plastic, the average of the six ratios.
3. Find v, the speed of light in the plastic, in m/s.