We look at the division of 643221 by 40 
We want to figure out the number of times 643221 can be divided by 40.

Let's proceed to step 1:
The number 40 fits into 6 0 times, leaving 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.
Take the next digit (4) from the dividend and append it to 6, then repeat: 64 / 40

Going ahead to step 2:
40 goes into 64 1 times with a remainder of 24.
The number 1 becomes the next digit in our result. 
Result so far: 1.0
The remainder is 24 after subtracting 40 from 64.
Append the next digit (3) from the dividend to 24 and continue with: 243 / 40

Advancing to step 3:
243 divided by 40 is 6 with a remainder of 3.
Put 6 as the next digit of the answer. 
Result so far: 16.0
If we take 240 away from 243, we end up with 3.
Fetch the next digit (2) from the dividend, attach it to 3 and continue: 32 / 40

Going ahead to step 4:
40 can be fit into 32 0 times, resulting in a remainder of 32.
Record the quotient 0 as the next digit in the result. 
Result so far: 160.0
Deduct 0 from 32 and we're left with 32.
Fetch the next digit (2) from the dividend, attach it to 32 and continue: 322 / 40

Step 5:
40 goes into 322 8 times with a remainder of 2.
The number 8 becomes the next digit in our result. 
Result so far: 1608.0
Deduct 320 from 322 and we're left with 2.
Bring next digit (1) of the dividend behind the 2 and repeat the process: 21 / 40

Moving on to step 6:
40 can be fit into 21 0 times, resulting in a remainder of 21.
Write down 0 as next digit of the result. 
Result so far: 16080.0
If we take 0 away from 21, we end up with 21.
Since there are no more digits in the dividend, we add a zero to the remainder making it 210, and continue the process.

Let's proceed to step 7:
40 goes into 210 5 times with a remainder of 10.
The number 5 becomes the next digit in our result. 
Result so far: 16080.5
The remainder is 10 after subtracting 200 from 210.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Advancing to step 8:
40 goes into 100 2 times with a remainder of 20.
Write down 2 as next digit of the result. 
Result so far: 16080.52
If we subtract 80 from 100, we 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 9:
The number 40 fits into 200 5 times, leaving a remainder of 0.
The number 5 becomes the next digit in our result. 
Result so far: 16080.525
If we take 200 away from 200, we end up with 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

On to step 10:
If we divide 0 by 40, we get 0 and a remainder of 0.
Put 0 as the next digit of the answer. 
Result so far: 16080.525
The remainder is 0 after subtracting 0 from 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

Advancing to step 11:
If we divide 0 by 40, we get 0 and a remainder of 0.
Use 0 as the next digit of our solution. 
Result so far: 16080.525
Deduct 0 from 0 and we're left with 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

The quotient of the division is 16080.525, and the remainder is 0.0.