We need to calculate molar mass of empirical formula and compare it with real molar mass
1) M(C6H8O)==6*M(C) +8*M(H) + M(O)=12*6+8*1+16= 96 g/mol
2) compare with real molar mass 290/96≈ 3
Real Molar mass is 3 times more, so the number of atom of each element in molecular formula will be 3 times more
3) C(6*3)H(8*3)O(1*3)
C18H24O3 - molecular formula