Well, it takes 3 moles of oxygen to completely burn 2 moles of methyl...
So for every 2 moles of methyl, you need 1.5 times as much oxygen (3 divided by 2)
That makes your ratio 1 : 1.5
You need 1.33 moles of methyl so you multiply both sides of the ratio by 1.33 = 1.33 : 1.995
1.995 moles of oxygen are needed
