You have been given the storm's velocity.
There are two major types of anatomy. Gross (macroscopic) anatomy is the study of anatomical structures that can be seen by the eye, such as the external and internal bodily organs. Microscopic anatomy is the study of tiny anatomical structures such as tissues and cells.
The two different isotopes have weights :
w1 = 78.918 amu
w2 = 80.916 amu
average weight w3 = 79.903 amu
The mixing of two components can be modeled as
let the fraction of w1 be 'x'
hence 
now this is a linear equation in 'x'. Substituting the values we get
x = 0.507
hence the percentage of Br79 = 50.7% and the percentage of BR81 = 49.3%