We're dividing 643865 by 21 
Let's see how many times 21 fits into 643865.

Let's proceed to step 1:
If we divide 6 by 21, we get 0 and a remainder of 6.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
If we take 0 away from 6, we end up with 6.
Take the next digit (4) from the dividend and append it to 6, then repeat: 64 / 21

Moving on to step 2:
64 divided by 21 is 3 with a remainder of 1.
Put 3 as the next digit of the answer. 
Result so far: 3.0
Deduct 63 from 64 and we're left with 1.
Bring next digit (3) of the dividend behind the 1 and repeat the process: 13 / 21

Advancing to step 3:
21 goes into 13 0 times with a remainder of 13.
Write down 0 as next digit of the result. 
Result so far: 30.0
Deduct 0 from 13 and we're left with 13.
Append the next digit (8) from the dividend to 13 and continue with: 138 / 21

Advancing to step 4:
The number 21 fits into 138 6 times, leaving a remainder of 12.
Record the quotient 6 as the next digit in the result. 
Result so far: 306.0
The remainder is 12 after subtracting 126 from 138.
Take the next digit (6) from the dividend and append it to 12, then repeat: 126 / 21

Step 5:
126 divided by 21 is 6 with a remainder of 0.
The next digit of our result is 6. 
Result so far: 3066.0
If we subtract 126 from 126, we get 0.
Take the next digit (5) from the dividend and append it to 0, then repeat: 5 / 21

Moving on to step 6:
21 can be fit into 5 0 times, resulting in a remainder of 5.
Use 0 as the next digit of our solution. 
Result so far: 30660.0
Subtract 0 from 5 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.

Advancing to step 7:
The number 21 fits into 50 2 times, leaving a remainder of 8.
The number 2 becomes the next digit in our result. 
Result so far: 30660.2
If we subtract 42 from 50, we 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.

Advancing to step 8:
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: 30660.23
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 9:
If we divide 170 by 21, we get 8 and a remainder of 2.
The number 8 becomes the next digit in our result. 
Result so far: 30660.238
Subtract 168 from 170 to 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.

Going ahead to step 10:
21 can be fit into 20 0 times, resulting in a remainder of 20.
The number 0 becomes the next digit in our result. 
Result so far: 30660.238
Subtract 0 from 20 to get 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Moving on to step 11:
200 divided by 21 is 9 with a remainder of 11.
The next digit of our result is 9. 
Result so far: 30660.23809
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 12:
21 can be fit into 110 5 times, resulting in a remainder of 5.
Write down 5 as next digit of the result. 
Result so far: 30660.238095
Subtracting 105 from 110 leaves us with 5.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Advancing to step 13:
21 goes into 50 2 times with a remainder of 8.
The number 2 becomes the next digit in our result. 
Result so far: 30660.2380952
Subtract 42 from 50 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 14:
80 divided by 21 is 3 with a remainder of 17.
Use 3 as the next digit of our solution. 
Result so far: 30660.23809523
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.

The final result is 30660.23809523 with a remainder of 1.7e-08.