15.1 A can of coffee is shared by person A and person B, and they finish it together in 10 days. If person A drinks it alone, it takes 12 days. 1 pound of tea is shared by person A and person B, and they finish it together in 12 days. If person B drinks it alone, it takes 20 days. Assuming that person A will never drink coffee when there is tea, and person B will never drink tea when there is coffee. How many days will it take for the two to finish 1 pound of tea and 1 can of coffee together?
Three, 15. It is known that A drinks $\frac{1}{30}$ of 1 catty of tea every day, and B drinks $\frac{1}{60}$ of 1 can of coffee every day.
After 30 days, A finishes the tea while B only drinks half a can of coffee, and the remaining half can of coffee is drunk by A and B together in 5 days. Therefore, it takes a total of 35 days to finish both the coffee and the tea.