Profit = Sales − Cost.
From the graph:
- Jan: Sales $\approx 32$, Cost $\approx 30$ → Profit $\approx 2$
- Mar: Sales $\approx 33$, Cost $\approx 31$ → Profit $\approx 2$
- May: Sales $\approx 36$, Cost $\approx 33$ → Profit $\approx 3$
- Jul: Sales $\approx 38$, Cost $\approx 35$ → Profit $\approx 3$
- Sep: Sales $\approx 40$, Cost $\approx 36$ → Profit $\approx 4$
- Nov: Sales $\approx 41$, Cost $\approx 39$ → Profit $\approx 2$
Highest profit is in September.