Moles of CO₂:

$\mathrm{Moles}=\frac{17.6 \mathrm{g}}{44 \mathrm{g}/\mathrm{mol}}=0.4 \mathrm{mol}$

Moles of H₂O:

$\mathrm{Moles}=\frac{7.2 \mathrm{g}}{18 \mathrm{g}/\mathrm{mol}}=0.4 \mathrm{mol}$

General combustion reaction:

${\mathrm{C}}_{\mathrm{x}}{\mathrm{H}}_{\mathrm{y}}+\frac{1}{2}\left(\mathrm{x}+\frac{\mathrm{y}}{2}\right){\mathrm{O}}_2\to {\mathrm{xCO}}_2+\frac{\mathrm{y}}{2}{\mathrm{H}}_2\mathrm{O}$

Hence, x is 0.4 and y is 0.8; formula becomes C₄H₈.