Use the data given in the following table to calculate the molar mass of naturally occurring organ:
Isotope             Isotopic molar mass                      Abundance
${}^{36}Ar$                       35.96 ${\text{g mol}}^{-1}$                              0.337%        
${}^{38}Ar$                       37.96 ${\text{g mol}}^{-1}$                              0.063%