Answer
See the answer below.
Work Step by Step
a) 158 peak: $^{79}Br_2$;
160 peak: $^{79}Br^{81}Br$;
162 peak: $^{81}Br_2$;
b) Since both isotopes have a relative abundance of roughly 50%, the peaks are proportional to the number of possible combinations between them.
The 160 peak has two possible combinations ($^{79}Br^{81}Br$ and $^{81}Br^{79}Br$) vs one for each of the other two, which explains the ratio of intensities of the peaks (1:2:1).
