Let's divide 215129 by 21
Let's see how many times 21 fits into 215129.

Step 1:
2 divided by 21 is 0 with a remainder of 2.
The next digit of our result is 0. 
Result so far: 0.0
If we take 0 away from 2, we end up with 2.
Grab the next digit (1) from the dividend, add it to 2, then carry on: 21 / 21

Moving on to step 2:
21 can be fit into 21 1 times, resulting in a remainder of 0.
The number 1 becomes the next digit in our result. 
Result so far: 1.0
The remainder is 0 after subtracting 21 from 21.
Append the next digit (5) from the dividend to 0 and continue with: 5 / 21

Step 3:
21 can be fit into 5 0 times, resulting in a remainder of 5.
Record the quotient 0 as the next digit in the result. 
Result so far: 10.0
If we take 0 away from 5, we end up with 5.
Bring next digit (1) of the dividend behind the 5 and repeat the process: 51 / 21

On to step 4:
The number 21 fits into 51 2 times, leaving a remainder of 9.
Put 2 as the next digit of the answer. 
Result so far: 102.0
The remainder is 9 after subtracting 42 from 51.
Take the next digit (2) from the dividend and append it to 9, then repeat: 92 / 21

Advancing to step 5:
92 divided by 21 is 4 with a remainder of 8.
The number 4 becomes the next digit in our result. 
Result so far: 1024.0
Subtract 84 from 92 to get 8.
Append the next digit (9) from the dividend to 8 and continue with: 89 / 21

Going ahead to step 6:
If we divide 89 by 21, we get 4 and a remainder of 5.
The next digit of our result is 4. 
Result so far: 10244.0
Subtracting 84 from 89 leaves us with 5.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Advancing to step 7:
When dividing 50 by 21, we get 2 with a remainder of 8.
Use 2 as the next digit of our solution. 
Result so far: 10244.2
Subtracting 42 from 50 leaves us with 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Advancing to step 8:
The number 21 fits into 80 3 times, leaving a remainder of 17.
The number 3 becomes the next digit in our result. 
Result so far: 10244.23
Subtracting 63 from 80 leaves us with 17.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

Let's proceed to step 9:
170 divided by 21 is 8 with a remainder of 2.
The next digit of our result is 8. 
Result so far: 10244.238
Subtracting 168 from 170 leaves us with 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

Going ahead to step 10:
The number 21 fits into 20 0 times, leaving a remainder of 20.
Put 0 as the next digit of the answer. 
Result so far: 10244.238
Subtracting 0 from 20 leaves us with 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Step 11:
21 goes into 200 9 times with a remainder of 11.
The next digit of our result is 9. 
Result so far: 10244.23809
Deduct 189 from 200 and we're left with 11.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

On to step 12:
When dividing 110 by 21, we get 5 with a remainder of 5.
The next digit of our result is 5. 
Result so far: 10244.238095
Subtract 105 from 110 to get 5.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Let's proceed to step 13:
21 goes into 50 2 times with a remainder of 8.
The next digit of our result is 2. 
Result so far: 10244.2380952
Deduct 42 from 50 and we're left with 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Moving on to step 14:
The number 21 fits into 80 3 times, leaving a remainder of 17.
Record the quotient 3 as the next digit in the result. 
Result so far: 10244.23809523
Subtract 63 from 80 to get 17.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

After the division, we end up with 10244.23809523 and a remainder of 1.7e-08.