Answer
6.941 amu
Work Step by Step
We multiply the mass of the isotope and its relative abundance (shown as a decimal). And then we add the products together.
Isotope 1: mass= 6.015 amu (7.5%)
Isotope 2: mass= 7.016 amu (92.5%)
= 6.015 (7.5%) + 7.016 (92.5%)
= 6.015 (0.075%) + 7.016 (0.925%)
= 6.941 amu
