Since X is 1 g, therefore O must be 0.1 g. Therefore:
moles O = 0.1 g / (16 g / mol) = 0.00625 mol
We can see that for every 3 moles of O, there are 2 moles of X, therefore:
moles X = 0.00625 mol O (3 moles X / 2 moles O) = 0.009375 mol
Molar mass X = 1 g / 0.009375 mol
Molar mass X = 106.67 g/mol