First find the moles
moles of the calcium= 72.8 / 40
moles of calcium in 72.8g = 1.82mol
number of atoms= moles x Avogadro constant
atoms = 1.82 x 6.02x10+23
so the number of atoms is 1.096x10+24
True I think is the answer
N2H4 is 28.014gmol+4.032gmol=32.046gmol