I looked on a solubility chart to answer this question, and hydroxides are generally insoluble (with some exceptions of course). However, it says to consider as an insoluble substance, though it may be moderately soluble.
The answer that you are most likely looking for is: Yes, a precipitate does form - this is due to the double placement reaction:
I got this answer through stoichiometry. For every 1 mole of Mg, 2 moles of CuBr are consumed. Because of this, multiply the moles of Mg by 2. Then, convert moles to grams.