On a pressure-volume graph a gas goes from A (1.5 L, 4.6 × 10⁵ Pa) to B (3.5 L, 1.8 × 10⁵ Pa) along…

Step 1. Straight line. $\tfrac12(4.6 + 1.8) \times 10^{5}\ \text{Pa} \times 2.0 \times 10^{-3}\ \text{m}^3 = 640\ \text{J}$.

Step 2. High path. All the expansion is at $4.6 \times 10^{5}\ \text{Pa}$: $4.6 \times 10^{5}\ \text{Pa} \times 2.0 \times 10^{-3}\ \text{m}^3 = 920\ \text{J}$.

Step 3. Low path. Pressure falls first, then it expands at $1.8 \times 10^{5}\ \text{Pa}$: $360\ \text{J}$.