Guys can you help me to understand this graph

The vertical line shows the amounts of units sold, and the corresponding points on the Average Cost (AC) and Average Revenue (AR) show the cost (R) and revenue (Q) per unit. Therefore, the profits are equal to (P-S) x (Q-R), which is the shaded area. The description underneath the graph seems to refer to the graph below (not shown in that photo). Hope this helps!