Answer
$9.5 \times10^{11} kg\ CO_{2} $
Work Step by Step
We need to find the total consumption of the cars and then the amount of carbon dioxide:
Annual production of $CO_{2}$ = $4 \times 10^{8} cars \times\frac{5000 mi}{1 car} \times \frac{1 gal}{20 mi} \times \frac{9.5 kg \ CO_{2}}{1 gal} = 9.5 \times10^{11} kg\ CO_{2} $
