$\therefore 0.72 \mathrm{g} \mathrm{H}_{2} \mathrm{O}$ contain $0.08 \mathrm{g} \mathrm{H}$
$44 \mathrm{g} \mathrm{CO}_{2}$ contain $12 \mathrm{g} \mathrm{C}$
$\therefore 3.08 \mathrm{g} \mathrm{CO}_{2}$ contain $0.84 \mathrm{g} \mathrm{C}$
$C: H=\frac{0.84}{12}: \frac{0.08}{1}=0.07: 0.08=7: 8$
$\therefore$ Empirical formula $=\mathrm{C}_{7} \mathrm{H}_{8}$