Answer:
a. What is the opportunity cost for Carlos to produce one more bushel of apples in terms of pears?
opportunity cost to produce 1 more bushel of apples = 30 / 15 = 2 bushels of pears
b. What is the opportunity cost for Donna to produce one more bushel of apples in terms of pears?
opportunity cost to produce 1 more bushel of apples = 20 / 5 = 4 bushels of pears
c. What would Donna and Carlos agree to as acceptable terms of trade?
Donna has a comparative advantage in the production of pears, so she should produce pears and exchange them for apples produced by Carlos.
Any range between 1-2 pears (higher than 1, but lower than 2) exchanged for every apple would result in mutually beneficial trade.