Calculate the average atomic mass for element X(please help)

Wt Avg At Mass = 39.0229 amu

Explanation:

The Weight Average Atomic Mass in atomic mass units (amu) is the sum of the Weight Average Mass contributions of each isotopic mass. That is,

Wt. Avg. At. Mass (amu) = ∑ Wt. Avg. Contributions of each isotopic mass

Wt. Avg. Contribution = fractional abundance x isotopic mass(amu)

For this problem data:

Isotope   %Abundance     fractional         Isotopic             Wt Avg Isotopic

                                        abundance      mass(amu)        Contribution (amu)

   1                  9.67%           0.0967               38                      3.6746 amu

   2               78.68%           0.7868               39                    30.6852 amu

   3                 11.34%           0.1134                 40                      4.5360 amu

   4                  0.31%           0.0031                41                       0.1271  amu

Wt. Avg. Atomic Mass (amu) = ∑ Wt. Avg. Contributions  =  39.0229 amu