Jules wants to purchase a Royale with cheese from Vincent. Vincent is willing to offer this tasty burger for $3. The most Jules is willing to pay for the tasty burger is $8 (after all, his girlfriend is a vegetarian, so he doesn't get many opportunities for tasty burgers). a. How large are the potential gains from trade if Jules and Vincent agree to make this trade?

If the trade takes place at $4, how much producer surplus goes to Vincent? How much consumer surplus goes to Jules?*

4*4/2=8 <- I am wrong and I don't understand why I am wrong.

When do I find the area of rectangle below?