21129 ÷ 7 = 3018 R3
We're going to perform division on 21129 with 7 as the divisor.

Step 1:
7 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 / 7

Step 2:
7 goes into 21 3 times with a remainder of 0.
Write down 3 as next digit of of the result. 
Result so far: 3
Subtract 21 from 21 to get 0.
Bring next digit (1) of the dividend behind the 0 and repeat the process: 1 / 7

Step 3:
7 goes into 1 0 times with a remainder of 1.
Write down 0 as next digit of of the result. 
Result so far: 30
Subtract 0 from 1 to get 1.
Bring next digit (2) of the dividend behind the 1 and repeat the process: 12 / 7

Step 4:
7 goes into 12 1 times with a remainder of 5.
Write down 1 as next digit of of the result. 
Result so far: 301
Subtract 7 from 12 to get 5.
Bring next digit (9) of the dividend behind the 5 and repeat the process: 59 / 7

Step 5:
7 goes into 59 8 times with a remainder of 3.
Write down 8 as next digit of of the result. 
Result so far: 3018
Subtract 56 from 59 to get 3.

The final result is 3018 with a remainder of 3.