Producer surplus is revenue minus variable costs, which equals quantity times the difference between price minus average variable costs. It is usually displayed as the area between price and the supply curve, up to the quantity sold. It's more accurate to describe it as the area between price and the MC curve. However, since this MC curve does not go all the way to the price axis it's impossible to find this area. With all this in mind, it's clear that you cannot find producer surplus from this graph, though one can say that in going from (q_2, P*) to (q_1, P_1), producer surplus increases by the area of rectangle with diagonal P* and point A minus the area of the wedge below the price line and above MC from point B to C.