Find the number of 6 digit numbers that ends with 21 (eg. 537621), without repetition of digits

What is the number of five-digit numbers formed with 0, 1, 2, 3, 4 without any repetition of digits ?

Find the number of 3-digit numbers, formed with the digit (2,5,4,6) when repetition of the digits is allowed.

Find the number of 6-digit numbers using the digits 3,4,5,6,7,8 without repetition. How many of these numbers are (a) divisible by 5 (b) not divisible by 5

The sum of all five digit numbers formed with the digits 1,2,3,4,5 without repetition of digits are

Find the number of three-digit numbers formed by using digits 1,2,3,4,6,7,8,9 without repetition such that sum of digits of the numbers formed is even.