This is a limiting reagent (LR) problem. I know that because amounts are given for BOTH reactants.
C2H4 + HCl ==> CH3CH2Cl
Convert grams C2H2 to mols. mols = grams/molar mass
Do the same for HCl
Using the coefficients in the balanced equation convert mols C2H4 to mols product.
Do the same for mols HCl to mol product.
It is likely these two values will not agree which means one of them is not right; the correct answer in LR problems is ALWAYS the smaller value and the reagent producing that value is the LR.
Now convert mols of the product to grams. mols = g x molar mass. This is the theoretical yield.