Atomic mass and identifying the element?

Question

A certain metal oxide has the formula MO where M denotes the metal. A 39.46-g sample of the compound is strongly heated in an atmosphere of hydrogen to remove oxygen as water molecules. At the end, 31.70 g of the metal is left over. If O has atomic mass of 16.00 amu, calculate the atomic mass of M and identify the element

Answer 1

MO + H2 ==> M + H2O

the moles of MO 39.46/(M + 16) (M here is the atomic mass of M)
the moles of M 31.7 / M
we have the ratio :
39.46 / (M + 16) = 31.7 / M
solve for M we have M = 65.36
=> M is Zinc

Answer 2

oxygen has a molar mass of 16 g/mol and exists in a one to one ratio with the metal so subtract the mass of the oxygen from the total mass ie 39.46-31.70 = grams of oxygen removed
divide answer by 16g/mol and you will have the number of moles of oxygen which is equal to the number of moles of the metal. now you divide the mass of the metal (31.70 g) by the number of moles and you will have the molar mass of the metal