We look at the division of 10815050 by 21 
We want to figure out the number of times 10815050 can be divided by 21.

Advancing to step 1:
When dividing 1 by 21, we get 0 with a remainder of 1.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
If we subtract 0 from 1, we get 1.
Bring next digit (0) of the dividend behind the 1 and repeat the process: 10 / 21

Let's proceed to step 2:
21 can be fit into 10 0 times, resulting in a remainder of 10.
Put 0 as the next digit of the answer. 
Result so far: 0.0
The remainder is 10 after subtracting 0 from 10.
Include the next digit (8) from the dividend after 10, then repeat: 108 / 21

Advancing to step 3:
21 can be fit into 108 5 times, resulting in a remainder of 3.
Use 5 as the next digit of our solution. 
Result so far: 5.0
The remainder is 3 after subtracting 105 from 108.
Include the next digit (1) from the dividend after 3, then repeat: 31 / 21

Moving on to step 4:
When dividing 31 by 21, we get 1 with a remainder of 10.
Put 1 as the next digit of the answer. 
Result so far: 51.0
Subtracting 21 from 31 leaves us with 10.
Append the next digit (5) from the dividend to 10 and continue with: 105 / 21

Going ahead to step 5:
21 can be fit into 105 5 times, resulting in a remainder of 0.
Put 5 as the next digit of the answer. 
Result so far: 515.0
The remainder is 0 after subtracting 105 from 105.
Include the next digit (0) from the dividend after 0, then repeat: 0 / 21

Advancing to step 6:
When dividing 0 by 21, we get 0 with a remainder of 0.
Put 0 as the next digit of the answer. 
Result so far: 5150.0
Subtract 0 from 0 to get 0.
Include the next digit (5) from the dividend after 0, then repeat: 5 / 21

Going ahead to step 7:
When dividing 5 by 21, we get 0 with a remainder of 5.
Record the quotient 0 as the next digit in the result. 
Result so far: 51500.0
Subtract 0 from 5 to get 5.
Include the next digit (0) from the dividend after 5, then repeat: 50 / 21

Moving on to step 8:
The number 21 fits into 50 2 times, leaving a remainder of 8.
The next digit of our result is 2. 
Result so far: 515002.0
If we subtract 42 from 50, we get 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Going ahead to step 9:
21 goes into 80 3 times with a remainder of 17.
Record the quotient 3 as the next digit in the result. 
Result so far: 515002.3
If we take 63 away from 80, we end up 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.

Advancing to step 10:
21 can be fit into 170 8 times, resulting in a remainder of 2.
Write down 8 as next digit of the result. 
Result so far: 515002.38
The remainder is 2 after subtracting 168 from 170.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

On to step 11:
When dividing 20 by 21, we get 0 with a remainder of 20.
The number 0 becomes the next digit in our result. 
Result so far: 515002.38
Subtract 0 from 20 to get 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Moving on to step 12:
If we divide 200 by 21, we get 9 and a remainder of 11.
Write down 9 as next digit of the result. 
Result so far: 515002.3809
If we subtract 189 from 200, we get 11.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

Going ahead to step 13:
21 can be fit into 110 5 times, resulting in a remainder of 5.
Record the quotient 5 as the next digit in the result. 
Result so far: 515002.38095
Subtracting 105 from 110 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 14:
The number 21 fits into 50 2 times, leaving a remainder of 8.
The next digit of our result is 2. 
Result so far: 515002.380952
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.

Let's proceed to step 15:
If we divide 80 by 21, we get 3 and a remainder of 17.
The number 3 becomes the next digit in our result. 
Result so far: 515002.3809523
Deduct 63 from 80 and we're left 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.

Going ahead to step 16:
When dividing 170 by 21, we get 8 with a remainder of 2.
The number 8 becomes the next digit in our result. 
Result so far: 515002.38095238
If we subtract 168 from 170, we get 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

The final outcome is 515002.38095238, with a leftover of 2e-09.