We look at the division of 638628 by 21 
Our goal is to divide 638628 by 21.

Step 1:
If we divide 6 by 21, we get 0 and a remainder of 6.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
If we subtract 0 from 6, we get 6.
Fetch the next digit (3) from the dividend, attach it to 6 and continue: 63 / 21

Let's proceed to step 2:
21 can be fit into 63 3 times, resulting in a remainder of 0.
Record the quotient 3 as the next digit in the result. 
Result so far: 3.0
Deduct 63 from 63 and we're left with 0.
Fetch the next digit (8) from the dividend, attach it to 0 and continue: 8 / 21

On to step 3:
21 goes into 8 0 times with a remainder of 8.
Write down 0 as next digit of the result. 
Result so far: 30.0
If we subtract 0 from 8, we get 8.
Append the next digit (6) from the dividend to 8 and continue with: 86 / 21

Let's proceed to step 4:
21 goes into 86 4 times with a remainder of 2.
The next digit of our result is 4. 
Result so far: 304.0
If we subtract 84 from 86, we get 2.
Append the next digit (2) from the dividend to 2 and continue with: 22 / 21

On to step 5:
22 divided by 21 is 1 with a remainder of 1.
The number 1 becomes the next digit in our result. 
Result so far: 3041.0
Deduct 21 from 22 and we're left with 1.
Include the next digit (8) from the dividend after 1, then repeat: 18 / 21

On to step 6:
The number 21 fits into 18 0 times, leaving a remainder of 18.
The number 0 becomes the next digit in our result. 
Result so far: 30410.0
Subtracting 0 from 18 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.

Advancing to step 7:
180 divided by 21 is 8 with a remainder of 12.
Record the quotient 8 as the next digit in the result. 
Result so far: 30410.8
Deduct 168 from 180 and we're left 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.

Step 8:
21 goes into 120 5 times with a remainder of 15.
Put 5 as the next digit of the answer. 
Result so far: 30410.85
Subtract 105 from 120 to 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.

Going ahead to step 9:
If we divide 150 by 21, we get 7 and a remainder of 3.
Write down 7 as next digit of the result. 
Result so far: 30410.857
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.

On to step 10:
If we divide 30 by 21, we get 1 and a remainder of 9.
The number 1 becomes the next digit in our result. 
Result so far: 30410.8571
Subtracting 21 from 30 leaves us with 9.
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 11:
21 can be fit into 90 4 times, resulting in a remainder of 6.
Use 4 as the next digit of our solution. 
Result so far: 30410.85714
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.

Advancing to step 12:
If we divide 60 by 21, we get 2 and a remainder of 18.
Record the quotient 2 as the next digit in the result. 
Result so far: 30410.857142
The remainder is 18 after subtracting 42 from 60.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Advancing to step 13:
180 divided by 21 is 8 with a remainder of 12.
Record the quotient 8 as the next digit in the result. 
Result so far: 30410.8571428
Subtract 168 from 180 to get 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 14:
21 can be fit into 120 5 times, resulting in a remainder of 15.
Write down 5 as next digit of the result. 
Result so far: 30410.85714285
Deduct 105 from 120 and we're left with 15.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

The final result is 30410.85714285 with a remainder of 1.5e-08.