<span>5.75 moles
The formula for methyl tert-butyl ether is (CH3)3COCH3, so a single molecule has 5 carbon, 12 hydrogen, and 1 oxygen atoms. So for every 12 moles of hydrogen, there's 1 mole of oxygen. So simply divide the number of moles of hydrogen by 12 to get the number of moles of oxygen.
69.0 / 12 = 5.75
Therefore there's 5.75 moles of oxygen in the sample.</span>