Mr(MgSo4) = 24.305 + 32.065 + (4 * 15.999) = 120.366 g/mol
Mr(Al2(Co3)3) = (2 26.982) + (3 ((1 12.011) + (3 15.999))) = 226.982 + 343.034 = 9.094 + 129.102 = 138.196 g/mol
Mr(MgSo4) = 24.305 + 32.065 + (4 * 15.999) = 120.366 g/mol
Mr(Al2(Co3)3) = (2 26.982) + (3 ((1 12.011) + (3 15.999))) = 226.982 + 343.034 = 9.094 + 129.102 = 138.196 g/mol