To get the overall abundance of the compound, what we have to do is to simply multiply the abundance of each element of that compound in decimal form.
50.69% = 0.5069
75.77% = 0.7577
Therefore:
0.5069 * 0.7577 = 0.3840
Therefore the abundance of 79Br35Cl is about 38.40%
answer:
38.40%