In order to answer this question we will need to use the molar mass of Calcium bromide (CaBr2), which is 199.89 g/mol, now we can find how much of this mass is only Bromide, so what is the percentage of Bromide that makes up this whole compound, to do so we will also use the molar mass of Bromide (Br2) which is 159.8 g/mol
199.89 g/mol = 100% of the compound
159.8 g/mol = x %
x = roughly 80% (is like 79.9%)
So, regardless of the mass of CaBr2, bromide needs to be 80% of its mass, now solving our question
395 g = 100%
x grams = 80%
x = 316 grams is the mass of Bromide in the compound