1) Percentage of Oxygen is 100-40-6.67 = 53.33
Therefore if you divide each of the percentages by the relative atomic masses (40/12 , 6.67/1 , 53.33/16) you get 3.33:6.67:3.33 (C : H : O)
Which in its simplest form is 1:2:1, hence the empirical formula is 1:2:1 (CH2O)
You're told the Mr of the acid is 60 g/mol hence since the empirical formula is 30g/mol you can see that the empirical formula needs to be scaled by a factor of 2 so that its the same as the molecular formula. Hence the molecula formula is C2H4O2 (or ethanoic acid)
2) Total number of atoms in 6g of acid is therefore 6/60 moles of acid (0.1) which means the total number of molecules of acid is 0.1 x avogadro number = 6.022 x 10^22, hence the total number of atoms is this x8 since there are 8 atoms in each molcule
3)2 mol of acid produces 1 mol CO2. 2 mol acid is the same as 120g of acid hence if we used 8 grams of acid this is x15 less acid so the number of moles of CO2 produces will be fifteen times less (or 1/15)
And multiplying this by 24 (because there are 24 mol per dm^-3 at RTP) we can say that there must be 1.6dm^3 CO2 which is 1600cm^3
That should help.