The problem gives us the percentages for carbon and hydrogen in the unknown acid:
54.5 % carbon
9.10 % hydrogen
The difference until 100 % is oxygen:
36.4 % oxygen
Now we may calculate the empirical formula of the unknown acid:
First we divide each percentage by the atomic mass of each component:
carbon = 54.5 / 12 = 4.54
hydrogen = 9.1 / 1 = 9.1
oxygen = 36.4 / 16 = 2.28
Now we divide the answers to the smallest number, which is 2.28:
carbon = 4.54 / 2.28 = 2
hydrogen = 9.1 / 2.28 = 4
oxygen = 2.28 / 2.28 = 1
Now the empirical formula for the acid will be:
C₂H₄O₁
And molecular formula:
(C₂H₄O₁)ₓ , but here we do not have enough information to determine unknown "x".