You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
methyl 4-[[7-(2-ethoxy-2-oxoethoxy)-4-oxo-4a,5,6,7,8,8a-hexahydrochromen-3-yl]oxy]benzoate The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H24O8
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