A ray falls at 40° on a glass slab 6 cm thick, with n = 1.5…

Step 1. Inside. $\sin r = \dfrac{\sin 40^\circ}{1.5} = \dfrac{0.643}{1.5} = 0.429$, so $r = 25.4^\circ$.

Step 2. The pieces. $i - r = 14.6^\circ$, $\sin 14.6^\circ = 0.253$, and $\cos 25.4^\circ = 0.904$.

Step 3. The shift. $d = \dfrac{6\ \text{cm} \times 0.253}{0.904} = 1.68\ \text{cm}$.