My point was that its understandable that its not -$4, because revenue is supposed to be without costs. According to the screen and the tooltip together he's generating +3.5 steel, and consuming -3 iron because of the bonuses. So, $43*3.5 - $43*3.0 is the $21.5 you arrived at. So, I guess it is profit after all. I can't account for the remaining 1.5 with what we can see. Maybe the sale price is being adjusted by how much the price would decrease selling that 3.5 steel.
UPDATE: I was trying to rationalize the .5 extra steel coming from somewhere I can't figure, and lost sight of the fact that the $20 revenue would not be correct if all three steel mills were reporting $20. I have no idea how this calculation is working.