Answer
$\theta_4 = 35.3^{\circ}$
Work Step by Step
According to Snell's law:
$n_1~sin~\theta_1 = n_2~sin~\theta_2 = n_3~sin~\theta_3 = n_4~sin~\theta_4$
We can find $\theta_4$:
$n_1~sin~\theta_1 = n_4~sin~\theta_4$
$sin~\theta_4 = \frac{n_1~sin~\theta_1}{n_4}$
$\theta_4 = sin^{-1}~(\frac{n_1~sin~\theta_1}{n_4})$
$\theta_4 = sin^{-1}~(\frac{1.30~sin~40.1^{\circ}}{1.45})$
$\theta_4 = sin^{-1}~(0.57749)$
$\theta_4 = 35.3^{\circ}$
