Question

my last question is how do you determine the molecular formula of a covalent compound given its formula?

Answer 1

You're missing something here. You must have the molar mass, too.

CH2 is empirical formula. Molar mass is 42. CH2 is 14 (12+2), then 42/14 = 3 so there must be 3 units of CH2 or (CH2)3 = C3H6.