n = 3. (I know I'm answering this a week later, still hope this helps you understand the concept.) C17H14O7 has a molar mass of 330.29 g/mol. An empirical formula is essentially just a chemical formula simplified down to it's most common denominator of the subscripts. Dividing 990.87 g/mol by 330.29 g/mol gives us 3, the value of n. To go further, the chemical he was using was C51H42O21, or... (2R,2'R,2''R,3R,3'R,3''R,4R,4'R,4''S)-2,2',2''-Tris(3,4-dihydroxyphenyl)-4''-(2,4,6-trihydroxyphenyl)-3,3',3'',4,4',4''-hexahydro-2H,2'H,2''H-4,8':4',8''-terchromene-3,3',3'',5,5',5'',7,7',7''-nonol, whatever the hell that is.
