Answer
58.0% M in MO
Work Step by Step
If the M2O substance is 73.4% M by mass, then it is 26.6% oxygen by mass.
This means that if you had one mole of M2O:
26.6= 15.9994g O\div xg M2O\times 100
Or that 60.148 would be the grams of M2O in a mole.
60.148 - 15.9994= 44.15 as the mass of the 2M atoms; each M is 22.07 g/mol
So for MO: ?% M in MO = 22.07g M\div 22.07 + 15.9994g MO\times 100
= 58.0% M in MO