We look at the division of 63921139 by 21 
We're looking to find how many times 21 goes into 63921139.

Advancing to step 1:
When dividing 6 by 21, we get 0 with 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.
Append the next digit (3) from the dividend to 6 and continue with: 63 / 21

Step 2:
21 goes into 63 3 times with a remainder of 0.
Put 3 as the next digit of the answer. 
Result so far: 3.0
If we take 63 away from 63, we end up with 0.
Take the next digit (9) from the dividend and append it to 0, then repeat: 9 / 21

Moving on to step 3:
The number 21 fits into 9 0 times, leaving a remainder of 9.
Put 0 as the next digit of the answer. 
Result so far: 30.0
Subtracting 0 from 9 leaves us with 9.
Append the next digit (2) from the dividend to 9 and continue with: 92 / 21

Let's proceed to step 4:
21 can be fit into 92 4 times, resulting in a remainder of 8.
The number 4 becomes the next digit in our result. 
Result so far: 304.0
If we take 84 away from 92, we end up with 8.
Append the next digit (1) from the dividend to 8 and continue with: 81 / 21

On to step 5:
81 divided by 21 is 3 with a remainder of 18.
The number 3 becomes the next digit in our result. 
Result so far: 3043.0
Subtracting 63 from 81 leaves us with 18.
Append the next digit (1) from the dividend to 18 and continue with: 181 / 21

Advancing to step 6:
21 can be fit into 181 8 times, resulting in a remainder of 13.
Record the quotient 8 as the next digit in the result. 
Result so far: 30438.0
Deduct 168 from 181 and we're left with 13.
Grab the next digit (3) from the dividend, add it to 13, then carry on: 133 / 21

Advancing to step 7:
21 goes into 133 6 times with a remainder of 7.
The number 6 becomes the next digit in our result. 
Result so far: 304386.0
Deduct 126 from 133 and we're left with 7.
Fetch the next digit (9) from the dividend, attach it to 7 and continue: 79 / 21

Step 8:
79 divided by 21 is 3 with a remainder of 16.
Write down 3 as next digit of the result. 
Result so far: 3043863.0
Deduct 63 from 79 and we're left with 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

Going ahead to step 9:
The number 21 fits into 160 7 times, leaving a remainder of 13.
The number 7 becomes the next digit in our result. 
Result so far: 3043863.7
Subtracting 147 from 160 leaves us with 13.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

Let's proceed to step 10:
21 can be fit into 130 6 times, resulting in a remainder of 4.
Use 6 as the next digit of our solution. 
Result so far: 3043863.76
If we subtract 126 from 130, we get 4.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

Advancing to step 11:
The number 21 fits into 40 1 times, leaving a remainder of 19.
Write down 1 as next digit of the result. 
Result so far: 3043863.761
Subtract 21 from 40 to get 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Advancing to step 12:
If we divide 190 by 21, we get 9 and a remainder of 1.
The next digit of our result is 9. 
Result so far: 3043863.7619
If we take 189 away from 190, we end up with 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

On to step 13:
The number 21 fits into 10 0 times, leaving a remainder of 10.
Use 0 as the next digit of our solution. 
Result so far: 3043863.7619
The remainder is 10 after subtracting 0 from 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Let's proceed to step 14:
21 goes into 100 4 times with a remainder of 16.
The next digit of our result is 4. 
Result so far: 3043863.761904
If we subtract 84 from 100, we get 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

On to step 15:
If we divide 160 by 21, we get 7 and a remainder of 13.
Write down 7 as next digit of the result. 
Result so far: 3043863.7619047
The remainder is 13 after subtracting 147 from 160.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

Let's proceed to step 16:
If we divide 130 by 21, we get 6 and a remainder of 4.
Put 6 as the next digit of the answer. 
Result so far: 3043863.76190476
If we take 126 away from 130, we end up with 4.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

The final outcome is 3043863.76190476, with a leftover of 4e-09.