ANSWER
[tex]\begin{equation*} 40.0\degree \end{equation*}[/tex]EXPLANATION
To find the critical angle for the boundary, we have to apply the formula:
[tex]\theta=\sin^{-1}(\frac{n_r}{n_i})[/tex]where nr = refraction index = 1.33
ni = incident index = 2.07
Hence, the critical angle for the boundary is:
[tex]\begin{gathered} \theta=\sin^{-1}(\frac{1.33}{2.07}) \\ \theta=\sin^{-1}(0.6425) \\ \theta=40.0\degree \end{gathered}[/tex]That is the answer.
