what is the relative atomic mass of a hypothetical element that consists of the following isotopes in the indicated natural abundances?? pls help

Answer:
87.3
Explanation:
To calculate the relative atomic mass
((84.9*15)+(86.9*12.9)+(87.9*72.1))/15+12.9+72.1
(1273.5 + 1121.01 + 6337.59) / 100
8732.1/100
87.321 = 87.3