The formula unit is CH, so there is 1 H for every 1 C. Set up a table with the two elements and their atomic masses, which are also their molar masses. Guess at a value for the number of C atoms, at 12 g/mole each) that would take us close to 78.11 g/mole, without going over.
6 would get us to 72. The number of hydrogens is the same as the number of carbons, so add 6 to the molar mass of the compound. The sum of 72 (from the carbons) and 6 (from the hydrogens) is close enough, for me, to the 72.110 g/mole specified. I used rounded numbers for the atomic masses, so use the more precise values in your work.
That means there are 6 each of the carbon and hydrogen. The formula is C6H6.