I haven't checked all the arithmetic, but your approach looks right.
Question 2: if you spot that the molecular weights of propane and CO2 are both 44, then the mass ratio equals the mole ratio. But your procedure is right in the general case.
Question 3: balanced equation requires 3O2, not 6, but it doesn't affect the answer.
Question 4: moles octane should be multiplied by 25/2, not 2/25, but you got the right answer.
Question 5: "vinegar" is of course not pure acetic acid, but in the absence of any information on the strength of the "vinegar", you can only do what you have done.