The nearest ten thousand to 16,500 is 20,000. So it is rounded up to 20,000.
Because 16,500 is more nearest to 20,000 than 10,000, a the second digit after 1 is 6 which is greater than 5 and close to 10 than 1. if it is less than 5, for example if the number is 14,500 then the number will be rounded to 10,000 as that one is more closest than 20,000.
But here 16,500 is rounded to 20,000.