M = 12x12+22x1+11x16 = 342 g/mol
342g ........ 144g C ............... 22g H .................. 176g O
100g (%) ...... x% ................ y% ........................... z%
x = 100x144/342 = 42,10% C
y = 22x100/342 = 6,43% H
z = 176x100/342 = 51,46% O