First you divide each mass by the mass number of the element:
Cobalt 1.216 / 59 = 0.02
Oxygen 0.495 / 32 = 0.03
Then the result is divided by the lowest number:
Cobalt 0.02 / 0.02 = 1
Oxygen 0.03 / 0.02 = 1.5
After that you multiply with a number to obtain an integer number:
Cobalt 1 × 2 = 2
Oxygen 1.5 × 2 = 3
The empirical formula of the oxide:
Co[tex]_{2}[/tex]O[tex]_{3}[/tex]
