Let x be a smallest number which when added to 2000 and resultant number is exactly divisible by 12,16,18,21 Find sum of digit of

Let, x be the smallest number, which when added to 2000 makes the resulting number divisible by 12, 16, 18 and 21. The sum of the digits of x is:

The least number that must be added to 3105 to get a number exactly divisible by 21.

which smallest number should be added to 872 so that it is exactly divisible by 3 ?

The least number that should be added to 2055 , so that the sum is exactly divisible by 27 is

Find the least number which should be added to 2497 so that the sum is exactly divisible by 5,6,4and 3