We look at the division of 15525108 by 21 
Let's see how many times 21 fits into 15525108.

Let's proceed to step 1:
If we divide 1 by 21, we get 0 and a remainder of 1.
Write down 0 as next digit of the result. 
Result so far: 0.0
Deduct 0 from 1 and we're left with 1.
Take the next digit (5) from the dividend and append it to 1, then repeat: 15 / 21

Moving on to step 2:
When dividing 15 by 21, we get 0 with a remainder of 15.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
The remainder is 15 after subtracting 0 from 15.
Fetch the next digit (5) from the dividend, attach it to 15 and continue: 155 / 21

On to step 3:
21 can be fit into 155 7 times, resulting in a remainder of 8.
Record the quotient 7 as the next digit in the result. 
Result so far: 7.0
If we take 147 away from 155, we end up with 8.
Include the next digit (2) from the dividend after 8, then repeat: 82 / 21

Moving on to step 4:
The number 21 fits into 82 3 times, leaving a remainder of 19.
The number 3 becomes the next digit in our result. 
Result so far: 73.0
Subtract 63 from 82 to get 19.
Bring next digit (5) of the dividend behind the 19 and repeat the process: 195 / 21

On to step 5:
When dividing 195 by 21, we get 9 with a remainder of 6.
The next digit of our result is 9. 
Result so far: 739.0
Subtract 189 from 195 to get 6.
Take the next digit (1) from the dividend and append it to 6, then repeat: 61 / 21

On to step 6:
The number 21 fits into 61 2 times, leaving a remainder of 19.
The number 2 becomes the next digit in our result. 
Result so far: 7392.0
If we subtract 42 from 61, we get 19.
Take the next digit (0) from the dividend and append it to 19, then repeat: 190 / 21

On to step 7:
21 goes into 190 9 times with a remainder of 1.
Put 9 as the next digit of the answer. 
Result so far: 73929.0
Subtracting 189 from 190 leaves us with 1.
Grab the next digit (8) from the dividend, add it to 1, then carry on: 18 / 21

Step 8:
21 can be fit into 18 0 times, resulting in a remainder of 18.
Use 0 as the next digit of our solution. 
Result so far: 739290.0
The remainder is 18 after subtracting 0 from 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Step 9:
180 divided by 21 is 8 with a remainder of 12.
Use 8 as the next digit of our solution. 
Result so far: 739290.8
The remainder is 12 after subtracting 168 from 180.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

Going ahead to step 10:
21 goes into 120 5 times with a remainder of 15.
The next digit of our result is 5. 
Result so far: 739290.85
If we subtract 105 from 120, we get 15.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

On to step 11:
21 goes into 150 7 times with a remainder of 3.
Put 7 as the next digit of the answer. 
Result so far: 739290.857
Subtracting 147 from 150 leaves us with 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Advancing to step 12:
The number 21 fits into 30 1 times, leaving a remainder of 9.
Use 1 as the next digit of our solution. 
Result so far: 739290.8571
The remainder is 9 after subtracting 21 from 30.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

Going ahead to step 13:
If we divide 90 by 21, we get 4 and a remainder of 6.
Record the quotient 4 as the next digit in the result. 
Result so far: 739290.85714
If we take 84 away from 90, we end up with 6.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

On to step 14:
The number 21 fits into 60 2 times, leaving a remainder of 18.
The next digit of our result is 2. 
Result so far: 739290.857142
Subtracting 42 from 60 leaves us with 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Let's proceed to step 15:
21 can be fit into 180 8 times, resulting in a remainder of 12.
Use 8 as the next digit of our solution. 
Result so far: 739290.8571428
If we take 168 away from 180, we end up with 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

On to step 16:
120 divided by 21 is 5 with a remainder of 15.
Write down 5 as next digit of the result. 
Result so far: 739290.85714285
The remainder is 15 after subtracting 105 from 120.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

Our division results in 739290.85714285 with a remaining 1.5e-08.