Zinc nitrate has a chemical formula of Zn(NO3)2. Molar mass = Zn+2N+6O = 65+28+96=189g/mole, because Zn=65, N=14 and O=16. These are approximate atomic weights.
More accurate values are: Zn=65.39, N=14.01, O=16.00, zinc nitrate molar mass=189.41g/mole approx.