We look at the division of 643658 by 21 
Let's see how many times 21 fits into 643658.

Moving on to step 1:
21 goes into 6 0 times with a remainder of 6.
Put 0 as the next digit of the answer. 
Result so far: 0.0
If we take 0 away from 6, we end up with 6.
Include the next digit (4) from the dividend after 6, then repeat: 64 / 21

Advancing to step 2:
21 can be fit into 64 3 times, resulting in a remainder of 1.
The next digit of our result is 3. 
Result so far: 3.0
If we take 63 away from 64, we end up with 1.
Bring next digit (3) of the dividend behind the 1 and repeat the process: 13 / 21

On to step 3:
The number 21 fits into 13 0 times, leaving a remainder of 13.
Put 0 as the next digit of the answer. 
Result so far: 30.0
If we subtract 0 from 13, we get 13.
Fetch the next digit (6) from the dividend, attach it to 13 and continue: 136 / 21

Let's proceed to step 4:
When dividing 136 by 21, we get 6 with a remainder of 10.
The next digit of our result is 6. 
Result so far: 306.0
If we subtract 126 from 136, we get 10.
Include the next digit (5) from the dividend after 10, then repeat: 105 / 21

Advancing to step 5:
21 goes into 105 5 times with a remainder of 0.
Write down 5 as next digit of the result. 
Result so far: 3065.0
If we subtract 105 from 105, we get 0.
Fetch the next digit (8) from the dividend, attach it to 0 and continue: 8 / 21

Moving on to step 6:
21 can be fit into 8 0 times, resulting in a remainder of 8.
Use 0 as the next digit of our solution. 
Result so far: 30650.0
Subtract 0 from 8 to 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 7:
21 can be fit into 80 3 times, resulting in a remainder of 17.
Use 3 as the next digit of our solution. 
Result so far: 30650.3
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 8:
When dividing 170 by 21, we get 8 with a remainder of 2.
Record the quotient 8 as the next digit in the result. 
Result so far: 30650.38
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.

Let's proceed to step 9:
The number 21 fits into 20 0 times, leaving a remainder of 20.
Use 0 as the next digit of our solution. 
Result so far: 30650.38
Deduct 0 from 20 and we're left 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.

Advancing to step 10:
21 goes into 200 9 times with a remainder of 11.
Use 9 as the next digit of our solution. 
Result so far: 30650.3809
Subtract 189 from 200 to 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.

Moving on to step 11:
If we divide 110 by 21, we get 5 and a remainder of 5.
The number 5 becomes the next digit in our result. 
Result so far: 30650.38095
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.

On to step 12:
The number 21 fits into 50 2 times, leaving a remainder of 8.
The next digit of our result is 2. 
Result so far: 30650.380952
If we take 42 away from 50, we end up 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.

On to step 13:
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: 30650.3809523
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.

Advancing to step 14:
170 divided by 21 is 8 with a remainder of 2.
Record the quotient 8 as the next digit in the result. 
Result so far: 30650.38095238
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.

The final result is 30650.38095238 with a remainder of 2e-09.