1. Find the empirical formula mass:

* C: 3 atoms * 12.01 g/mol = 36.03 g/mol

* H: 4 atoms * 1.01 g/mol = 4.04 g/mol

* Empirical formula mass = 36.03 + 4.04 = 40.07 g/mol

2. Calculate the ratio of molecular weight to empirical formula mass:

* Ratio = Molecular weight / Empirical formula mass

* Ratio = 120 g/mol / 40.07 g/mol

* Ratio ≈ 3

3. Multiply the subscripts in the empirical formula by the ratio:

* C3H4 * 3 = C9H12

Therefore, the molecular formula of the compound is C9H12.