A7.36 g sample of copper is contaminated with a additional 0.51 g sample of zinc. suppose an atomic mass measurement was performed on this sample. what would be the measured atomic mass?

The average molecular weight of the mixture can be calculated using this formula:
MWav = x1MW1 + x2MW2

Where x is the mass fraction of the components of the mixture, in this case, copper (63.546 g/mol) and zinc (65.38 g/mol).
 
x1 = 7.36 / (7.36+0.51)=0.935
x2 = 0.51 / (7.36+0.51)=0.065

So,
MWav = 0.935(63.546) + 0.065(65.38) = 63.665 g/mol

Adozen is 1221/12 = 1.751.75 x 12 = 21therefore, 1.75 is the answer.