Discover why two producers both end up better off by specializing in what they give up the least to make.
Discover why two parties both gain from specializing by comparative — not absolute — advantage.
Compare each producer's 'cost of 1 Good A'. Who gives up less Good B?
Before you act, predict what will happen. That producer has the comparative advantage in A — does it match who is better in absolute terms? Then do it — did your prediction match what happened?
Production possibilities
Each producer's PPF, plus the combined frontier once they specialize and trade. No-trade output sits inside the combined frontier; specialization reaches it.