A thin prism of crown glass has an angle of 5.0°…

Step 1. The mean deviation. $\delta_y = (1.517 - 1) \times 5.0^\circ = 2.59^\circ$.

Step 2. The angle of dispersion. $\delta_b - \delta_r = (1.522 - 1.514) \times 5.0^\circ = 0.040^\circ$.

Step 3. The dispersive power. $\omega = \dfrac{n_b - n_r}{n_y - 1} = \dfrac{0.008}{0.517} = 0.0155$.

Step 4. Under water. The relative index is $\dfrac{1.517}{1.33} = 1.141$. So $\delta = (1.141 - 1) \times 5.0^\circ = 0.70^\circ$.