We find the weight of the empirical formula:
12.0107 + 2 x 1.00794 + 15.9994
= 30.03
Now, we divide the molecular weight by the weight of the empirical formula to find the number of times the empirical formula repeats:
90.09 / 30.03
= 3
The formula is 3(CH₂O)
C₃H₆O₃