The formula weight of a compound is simply equal to the
total molar mass.
The molar mass of each elements are:
Mg = 24.305 g/mol
N = 14.0067 g/mol
O = 15.999 g/mol
So the total molar mass is:
formula weight = 24.305 + 2 (14.0067) + 6 (15.999)
formula weight = 148.3 g/mol
