We're dividing 643858 by 21 
We want to divide 643858 by 21.

Advancing to step 1:
When dividing 6 by 21, we get 0 with a remainder of 6.
The next digit of our result is 0. 
Result so far: 0.0
Deduct 0 from 6 and we're left with 6.
Grab the next digit (4) from the dividend, add it to 6, then carry on: 64 / 21

Advancing to step 2:
If we divide 64 by 21, we get 3 and a remainder of 1.
Record the quotient 3 as the next digit in the result. 
Result so far: 3.0
The remainder is 1 after subtracting 63 from 64.
Include the next digit (3) from the dividend after 1, then repeat: 13 / 21

Step 3:
13 divided by 21 is 0 with a remainder of 13.
Use 0 as the next digit of our solution. 
Result so far: 30.0
If we subtract 0 from 13, we get 13.
Append the next digit (8) from the dividend to 13 and continue with: 138 / 21

Let's proceed to step 4:
21 goes into 138 6 times with a remainder of 12.
Put 6 as the next digit of the answer. 
Result so far: 306.0
Deduct 126 from 138 and we're left with 12.
Bring next digit (5) of the dividend behind the 12 and repeat the process: 125 / 21

Going ahead to step 5:
21 goes into 125 5 times with a remainder of 20.
The next digit of our result is 5. 
Result so far: 3065.0
Deduct 105 from 125 and we're left with 20.
Bring next digit (8) of the dividend behind the 20 and repeat the process: 208 / 21

Let's proceed to step 6:
When dividing 208 by 21, we get 9 with a remainder of 19.
Put 9 as the next digit of the answer. 
Result so far: 30659.0
Subtract 189 from 208 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.

Moving on to step 7:
The number 21 fits into 190 9 times, leaving a remainder of 1.
The next digit of our result is 9. 
Result so far: 30659.9
Deduct 189 from 190 and we're left 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.

Going ahead to step 8:
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: 30659.9
Subtract 0 from 10 to get 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Step 9:
21 can be fit into 100 4 times, resulting in a remainder of 16.
Write down 4 as next digit of the result. 
Result so far: 30659.904
If we take 84 away from 100, we end up 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.

Step 10:
160 divided by 21 is 7 with a remainder of 13.
Record the quotient 7 as the next digit in the result. 
Result so far: 30659.9047
If we subtract 147 from 160, we get 13.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

Going ahead to step 11:
21 goes into 130 6 times with a remainder of 4.
The next digit of our result is 6. 
Result so far: 30659.90476
Subtracting 126 from 130 leaves us 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.

Step 12:
When dividing 40 by 21, we get 1 with a remainder of 19.
The number 1 becomes the next digit in our result. 
Result so far: 30659.904761
The remainder is 19 after subtracting 21 from 40.
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 13:
21 goes into 190 9 times with a remainder of 1.
Put 9 as the next digit of the answer. 
Result so far: 30659.9047619
The remainder is 1 after subtracting 189 from 190.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Moving on to step 14:
If we divide 10 by 21, we get 0 and a remainder of 10.
Put 0 as the next digit of the answer. 
Result so far: 30659.9047619
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.

After the division, we end up with 30659.9047619 and a remainder of 1e-08.