We look at the division of 21129536 by 831 
We want to figure out the number of times 21129536 can be divided by 831.

Advancing to step 1:
The number 831 fits into 2 0 times, leaving a remainder of 2.
Write down 0 as next digit of the result. 
Result so far: 0.0
Subtracting 0 from 2 leaves us with 2.
Include the next digit (1) from the dividend after 2, then repeat: 21 / 831

Advancing to step 2:
When dividing 21 by 831, we get 0 with a remainder of 21.
Write down 0 as next digit of the result. 
Result so far: 0.0
Deduct 0 from 21 and we're left with 21.
Fetch the next digit (1) from the dividend, attach it to 21 and continue: 211 / 831

Going ahead to step 3:
211 divided by 831 is 0 with a remainder of 211.
Use 0 as the next digit of our solution. 
Result so far: 0.0
If we take 0 away from 211, we end up with 211.
Grab the next digit (2) from the dividend, add it to 211, then carry on: 2112 / 831

Let's proceed to step 4:
831 can be fit into 2112 2 times, resulting in a remainder of 450.
The number 2 becomes the next digit in our result. 
Result so far: 2.0
Subtracting 1662 from 2112 leaves us with 450.
Bring next digit (9) of the dividend behind the 450 and repeat the process: 4509 / 831

Going ahead to step 5:
831 goes into 4509 5 times with a remainder of 354.
Write down 5 as next digit of the result. 
Result so far: 25.0
Subtracting 4155 from 4509 leaves us with 354.
Include the next digit (5) from the dividend after 354, then repeat: 3545 / 831

Advancing to step 6:
831 goes into 3545 4 times with a remainder of 221.
Use 4 as the next digit of our solution. 
Result so far: 254.0
If we take 3324 away from 3545, we end up with 221.
Bring next digit (3) of the dividend behind the 221 and repeat the process: 2213 / 831

Going ahead to step 7:
When dividing 2213 by 831, we get 2 with a remainder of 551.
The next digit of our result is 2. 
Result so far: 2542.0
If we subtract 1662 from 2213, we get 551.
Include the next digit (6) from the dividend after 551, then repeat: 5516 / 831

Let's proceed to step 8:
831 can be fit into 5516 6 times, resulting in a remainder of 530.
Put 6 as the next digit of the answer. 
Result so far: 25426.0
The remainder is 530 after subtracting 4986 from 5516.
Since there are no more digits in the dividend, we add a zero to the remainder making it 5300, and continue the process.

Advancing to step 9:
5300 divided by 831 is 6 with a remainder of 314.
Write down 6 as next digit of the result. 
Result so far: 25426.6
Deduct 4986 from 5300 and we're left with 314.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3140, and continue the process.

On to step 10:
If we divide 3140 by 831, we get 3 and a remainder of 647.
The next digit of our result is 3. 
Result so far: 25426.63
If we take 2493 away from 3140, we end up with 647.
Since there are no more digits in the dividend, we add a zero to the remainder making it 6470, and continue the process.

Going ahead to step 11:
The number 831 fits into 6470 7 times, leaving a remainder of 653.
Use 7 as the next digit of our solution. 
Result so far: 25426.637
The remainder is 653 after subtracting 5817 from 6470.
Since there are no more digits in the dividend, we add a zero to the remainder making it 6530, and continue the process.

Moving on to step 12:
6530 divided by 831 is 7 with a remainder of 713.
The next digit of our result is 7. 
Result so far: 25426.6377
If we subtract 5817 from 6530, we get 713.
Since there are no more digits in the dividend, we add a zero to the remainder making it 7130, and continue the process.

The final result is 25426.6377 with a remainder of 0.00713.