In the U.S., the emissions limit for carbon monoxide in motorcycle engine exhaust is 12.0 g CO per km driven. What is this limit expressed in milligrams per mile (mg/mi)?

So $12.0$ $g$ $k {m}^{-} 1$ = $12.0$ $g$ $\times 1000$ $m g$ ${g}^{-} 1$ $k {m}^{-} 1$ = $12 , 000$ $m g$ $\cancel{k {m}^{-} 1}$ $\times$ $0.6213$ $\cancel{k m}$ $m {i}^{-} 1$, which is what? About $7.5$ $\times$ ${10}^{3}$ millgrams per mile? Check this please because I'm too lazy to find a calculator.
I'm sorry to have abbreviated mile to $m i$ (I did this because $m$ = metre!), but if you do the calculation you will get an answer in "milligrams per mile". But why would you want to do so?