There is 1. They are the same. An airplane travels the same mile that we do.
The letter "k" is used to denote the metric prefix kilo (1000), which is a metric prefix. you would not measure miles in kilomiles. But if you were to, 50k miles would be 50,000 miles.
Exactly 40 miles. Changing from lower case to upper case does not alter the distance!
3,309.91 miles.
I don't suppose you read your question before you posted it. The answer is 3471 miles!