You seem to be unclear about the definitions of the different types of formula. The empirical formula is the molar ratio, expressed in its lowest terms, of the elements present in the compound. To calculate this you do not need to know the molecular weight, and from it you cannot calculate the molecular weight of the compound.
The molecular formula gives the actual number of atoms of each element in a molecule of the compound; from it you can calculate the molecular weight. If you know the empirical formula and the molecular weight, the molecular formula can be found by multiplying the empirical formula by the ratio (molecuar weight/empirical formula weight).
You have done this for styrene, but get the terminology wrong; the empirical formula is CH and the molecular formula is C8H8.
Both questions ask for the empirical formula and give you enough data to calculate it. Neither asks for the molecular formula, so the molecular weight is not needed.