An Element Found in Another Galaxy Exists as Two Isotopes

Multiple Choice

An element found in another galaxy exists as two isotopes.If 80.0 percent of the atoms have an atomic mass of 80.00 atomic mass units and the other 20.0 percent have an atomic mass of 82.00 atomic mass units,what is the atomic mass of the element?

A) 81.0 atomic mass units
B) 64.0 atomic mass units
C) 80.4 atomic mass units
D) 16.4 atomic mass units
E) 81.6 atomic mass units