21159 ÷ 8 = 2644 R7
Let's divide 21159 by 8.

Step 1:
8 goes into 2 0 times with a remainder of 2.
Write down 0 as next digit of of the result. 
Result so far: 0
Subtract 0 from 2 to get 2.
Bring next digit (1) of the dividend behind the 2 and repeat the process: 21 / 8

Step 2:
8 goes into 21 2 times with a remainder of 5.
Write down 2 as next digit of of the result. 
Result so far: 2
Subtract 16 from 21 to get 5.
Bring next digit (1) of the dividend behind the 5 and repeat the process: 51 / 8

Step 3:
8 goes into 51 6 times with a remainder of 3.
Write down 6 as next digit of of the result. 
Result so far: 26
Subtract 48 from 51 to get 3.
Bring next digit (5) of the dividend behind the 3 and repeat the process: 35 / 8

Step 4:
8 goes into 35 4 times with a remainder of 3.
Write down 4 as next digit of of the result. 
Result so far: 264
Subtract 32 from 35 to get 3.
Bring next digit (9) of the dividend behind the 3 and repeat the process: 39 / 8

Step 5:
8 goes into 39 4 times with a remainder of 7.
Write down 4 as next digit of of the result. 
Result so far: 2644
Subtract 32 from 39 to get 7.

The final result is 2644 with a remainder of 7.