A thin crown glass prism has an angle of 10.0°…

Step 1. No colour spread. The spreads must be equal: $0.0080 \times 10.0^\circ = 0.017 \times A_2$. We want $A_2$, so $A_2 = 10.0^\circ \times \dfrac{0.0080}{0.017} = 4.71^\circ$.

Step 2. The deviation left. $0.517 \times 10.0^\circ - 0.620 \times 4.71^\circ = 5.17^\circ - 2.92^\circ = 2.25^\circ$. The beam is turned by $2.25^\circ$ and shows no colours.

Step 3. No deviation. The yellow deviations must be equal: $0.517 \times 10.0^\circ = 0.620 \times A_2$, so $A_2 = 10.0^\circ \times \dfrac{0.517}{0.620} = 8.34^\circ$.

Step 4. The spread left. $0.0080 \times 10.0^\circ - 0.017 \times 8.34^\circ = 0.080^\circ - 0.142^\circ = -0.062^\circ$. The size is $0.062^\circ$, and the flint prism now spreads the colours the other way.