Answer
${2*\pi*radius}$
$={2*3.142*6370}$
$=40029\approx 40000$ km
Work Step by Step
Since we know that 1 kilometer = 1000 m,
Earth's radius = 6370000 m= 6370 kilometers
The formula for the circumference is 2*$\pi$*radius,
Therefore,
$2*\pi*radius={2*3.142*6370}=40029\approx 40000$ km
