There must be the same number of oxygens on both sides of the equation:
On the LHS, only O2 has oxygen atoms in it and since the reaction coefficient (the big number in front of the formula) is X and there are two oxygen atoms in each O2 molecule, then there must be 2X oxygens on the LHS.
On the RHS, CO2 and H2O both have oxygens in them and using their reaction coefficients, there must be 2n + n = 3n oxygens.
So we have 2X = 3n ==> X = 3n/2
I agree, 192 g of O2 is 6 mol of oxygen (since O2 has a relative mass of 32 g/mol) and therefore the correct continuation would be to equate 6 with 3n/2 and solve for n, which you can use to deduce the formula of the hydrocarbon.