Final answer:
The opportunity cost of one banana is 4 fish for Ann and 1 fish for Bob, calculated by the alternative of what they can produce instead of a banana.
Step-by-step explanation:
To calculate the opportunity costs of one banana for Ann and Bob, you look at what alternative production is given up. For Ann, if she produces one less banana, she can produce 4 fish instead (since 10 bananas equal 40 fish). The opportunity cost of one banana for Ann is therefore 4 fish. For Bob, the trade-off is one-to-one; if he produces one less banana, he can catch 1 more fish. Thus, the opportunity cost of one banana for Bob is 1 fish.