For a gas, 35 ppm means that there are 35 units of carbon monoxide in a totla of 1,000,000 units of gas in total. This is equivalent to: 35/1,000,000 = 3.5 x 10^-5.
The actual sample, which has 2.09%, can also be written as 0.0209. Then we divide 0.0209 / 3.5 x 10^-5, which gives 597.14. So the sample of cigarette smoke has CO concentration nearly 600 times more than the standard allows.