Can anyone please help me with CHEM?

Question

I am not sure how to find the empiracal and molecular formuala for the following problem:

A common acid is an important chemical used in the manufacture of polyesters and plasticizers. It contains only C, H, and O. Combustion of 19.81 mg of the acid produces 41.88 mg CO(2) and 6.45 mg H(2)O. The molar mass of the acid is 166 g/mol.

Answer 1

The molar mass of CO2 equals 44 and the atomic mass of C equals 12, so 41.88 mg of CO2 contain:

41.88x12/44 = 11.42 mg of C

The molar mass of H2O equals 18 and the atomic mass of H equals 1, so 6.45 mg of H2O contain:

6.45x2/18 = 0.72 mg of H

The rest is the mass of oxygen: 19.81 - 11.42 - 0.72 = 7.67 mg of O.

Now in 19.81 mg of the substance we have 11.42 mg of C, 0.72 mg of H and 7.67 mg of O

In 166 g (1 mole) of the substance we have:

11.42x166/19.81 = 95.7 g of C or 95.7/12 = 8 mol C

0.72x166/19.81 = 6 g of H or 6/1 = 6 mol H, and

7.67x166/19.81 = 64.3 g of O or 64.3/16 = 4 mol O

So the molecular formula of the acid is: C8H6O4

(It must be HOOC-C6H4-COOH an aromatic bicarboxylic acid)