Hydrocarbon means the compound comprises Hydrogen and Carbon atoms.

% of H\(_2\) = 14.29
% of C = 100 - 14.29 = 85.71

Solving the empirical formula for the Hydrocarbon,

Atom of element  C  H

% by mass 85.71 14.29

Divide by their Atomic masses  \(\frac{85.71}{12}\) \(\frac{14.29}{1}\)

Divide through by the smaller number \(\frac{7.1425}{7.1425}\)  \(\frac{14.29}{7.1425}\)

Ratio  1 : 2

Empirical formula:  CH\(_2\)

Recall that (Empirical formula)x n =  Molecular mass

 (CH\(_2\))n = Molecular mass

We need to get the molecular mass.To do that, we were given the:

mass, m = 0.07g and V = 56 cm\(^3\)

But  Number of moles =  \(\frac{volume}{Molar Volume}\) = \(\frac{56}{22,400}\) = 0.0025 mole

N.B : At stp, Molar volume of all gases = 22.4dm\(^3\) or 22,400cm\(^3\)

Thus, n = \(\frac{m}{M}\) 

 M = \(\frac{m}{n}\) = \(\frac{0.07}{0.0025}\) = 28.

(CH\(_2\))n = Molecular mass

(12 + (1 x 2))n = 28

14n = 28

  n = \(\frac{28}{14}\) = 2

The formula for the hydrocarbon = (CH\(_2\))n = (CH\(_2\))\(_2\) = C\(_2\)H\(_4\)