Relative atomic mass?

Question

Find the relative atomic mass of nickel if 3.370g nickel was obtained by reduction of 4.286 g of the oxide (NiO).

Answer 1

1. subtract the two masses to get the number of grams of O.
2. divide this by 16 to get the moles of O.
3. this is also the number of moles of Ni.
4. Ar of Ni = mass of Ni/moles of Ni