Suppose the United States is currently producing 60 tons of hamburgers and 27 tons of tacos, and Mexico is currently producing 12 tons of hamburgers and 15 tons of tacos. If the United States and Mexico each specialize in producing only one good (the good for which each has a comparative advantage), then a total of ______ additional ton(s) of hamburgers can be produced for the two countries combined.
a) 57
b) 54
c) 48
d) 42