Determine the refractive index of a medium using experimental data and Snell's Law.

The problem describes an experiment to determine the refractive index of a medium. We need to answer questions 18 and 19 based on the provided steps and diagram.

Step 1: Analyze the experiment setup and relevant formulas.
The experiment involves a light ray passing through a medium (likely a glass block) and measuring distances $x_1 = KM$ and $x_2 = KJ$, and an angle $\alpha$. K is the intersection of the normal at point I (KJ) and the normal at point M (KM). The ray enters the medium at I with angle of incidence $\alpha$ and refracts, then travels to M and exits.

From Snell's Law, at the first surface