How is 4.3 x 10^-3 the answer to this question?
a sample of air from a home is found to contain 6.2 ppm of carbon monoxide. this means that if the total pressure is 695 torr, then the partial pressure of co .3 x 10^-3.

The partial pressure of CO2 is equal to the total pressure * molar fraction of CO2.

To give 4.3 * 10^-3, they are using molar fraction = 6.2 * 10^ - 6

Because, 695 * 6.2-10^-6 = 0.004309 = 4.309 * 10^-3 = 4.3 * 10^-3.

Then the new question is why the molar fraction is consideres to be the same ppm concentration. This is because ppm means parts per million, and in this case, they are considering that the parts are moles (usually it is grams, but it is not the case, given the result).

 6.2 ppm = 6.2 / 1,000,000 = 6.2*10^-6, which is the number used above to multiply the total pressure and get the partial pressure of CO2.

If you had not told me that the result was 4.3 * 10^-3, I had assumed that 6.2 was referred to grams and not moles and I had made a conversion using the molar masses of the air and the CO2 but, again, this is not the case.