Find the number of molecules of deuterium.?

The natural abundances of the two stable isotopes of hydrogen (hydrogen and deuterium) are 11H: 99.985 percent and 21H: 0.015 percent. ume that water exists as either H2O or D2O. Calculate the number of D2O molecules in exactly 159 mL of water. (Density = 1.00 g/mL.)