Hello, Katrina,
I believe I just answered a similar question. Please check there for a more detailed answer, if you need it.
The mass of oxygen is the difference of the total mass less the mass of Mn (conservation of mass). I divided each mass by that element's atomic mass, to give a weighted mass (0.041 for each). Since these numbers are very close, we may assume they are essentially equal, so I used the factor (1/0.04 or 24.54) to bring both numbers up to the nearest whole number. That gives us an empirical formula of simply MnO. This is also the chemical formula, since Mn(II) has two valence electrons and O needs two for a complete shell, so MnO is a chemically stable arrangement.
Bob
