Required reaction,

C_$$x$$H_$$y$$ + $$\left( {x + {y \over 4}} \right)$$O₂ $$ \to $$$$x$$CO₂ + $${{y \over 2}}$$H₂O

0.72 gm of H₂O = $${{{0.72} \over {18}}}$$ mole of H₂O = 0.04 mole of H₂O

In one H₂O molecule 2 hydrogen atoms present.

So in 0.04 mole of H₂O molecules 2$$ \times $$0.04 = 0.08 moles of H atoms present.

0.72 gm of CO₂ = $${{{3.08} \over {44}}}$$ mole of CO₂ = 0.07 mole of CO₂

And in one CO₂ molecule 1 C atom present.

So in 0.07 mole of CO₂ molecules 0.07$$\times$$1 = 0.07 moles of C atoms present

$$\therefore$$ C : H = 0.07 : 0.08 = 7 : 8

$$\therefore$$ Empirical formula of hydrocarbon = C₇H₈