Dena and Andrew find themselves on a deserted island. The only two activities available are fishing and finding pineapples. In a full day, Dena can catch 8 fish or find 12 pineapples or some linear combination of the two; in the same time, Andrew can catch 5 fish or find 10 pineapples or some linear combination of the two. What are each individual's marginal costs of fishing and finding pineapples?