For a glass, the refractive index depends on the wavelength: n = 1.5046 + 0.0042/λ², with λ in…

Step 1. Red. $n = 1.5046 + \dfrac{0.0042}{0.49} = 1.5132$. Then $r_1 = 32.8^\circ$, $r_2 = 27.2^\circ$, $e = 43.8^\circ$, and $\delta = 55^\circ + 43.8^\circ - 60^\circ = 38.8^\circ$.

Step 2. Violet. $n = 1.5046 + \dfrac{0.0042}{0.16} = 1.5309$. Then $r_1 = 32.4^\circ$, $r_2 = 27.6^\circ$, $e = 45.3^\circ$, and $\delta = 40.3^\circ$.

Step 3. The spread. $40.27^\circ - 38.81^\circ = 1.46^\circ$.