Ah you cant do this 4.165 * 0.55 = 2.29075 g
Its 55% by mole not by weight right? So you have to figure out what the moles are, then calculate the percentage of weight of BaCl2*2H2O, then convert it back to grams, then calculate weight of 2H2O.
You know there should be formulas for this in your textbook..