Answer to queston on Average atomic mass

The element rhenium(RE) has two naturally occurring isotypes, 185Re and 187 Re, with an average atomic mass of 186.956 amu.  Calculate the mass of 185 Re

The mass of 185Re = 185?? Do you mean the percentage of 185Re?

Let percentage oif 185Re = w, so percentage of 187Re = 100-w

(w/100) x 185 + ((100-w)/100) x 187 = 186.956

Solve for w