We're dividing 64391099 by 643 
We want to figure out the number of times 64391099 can be divided by 643.

Moving on to step 1:
When dividing 6 by 643, we get 0 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.
Take the next digit (4) from the dividend and append it to 6, then repeat: 64 / 643

On to step 2:
The number 643 fits into 64 0 times, leaving a remainder of 64.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Subtract 0 from 64 to get 64.
Bring next digit (3) of the dividend behind the 64 and repeat the process: 643 / 643

Step 3:
643 goes into 643 1 times with a remainder of 0.
Write down 1 as next digit of the result. 
Result so far: 1.0
Subtracting 643 from 643 leaves us with 0.
Bring next digit (9) of the dividend behind the 0 and repeat the process: 9 / 643

On to step 4:
643 goes into 9 0 times with a remainder of 9.
Record the quotient 0 as the next digit in the result. 
Result so far: 10.0
If we take 0 away from 9, we end up with 9.
Grab the next digit (1) from the dividend, add it to 9, then carry on: 91 / 643

Let's proceed to step 5:
91 divided by 643 is 0 with a remainder of 91.
Record the quotient 0 as the next digit in the result. 
Result so far: 100.0
The remainder is 91 after subtracting 0 from 91.
Include the next digit (0) from the dividend after 91, then repeat: 910 / 643

Moving on to step 6:
643 can be fit into 910 1 times, resulting in a remainder of 267.
Record the quotient 1 as the next digit in the result. 
Result so far: 1001.0
Deduct 643 from 910 and we're left with 267.
Include the next digit (9) from the dividend after 267, then repeat: 2679 / 643

Let's proceed to step 7:
If we divide 2679 by 643, we get 4 and a remainder of 107.
Use 4 as the next digit of our solution. 
Result so far: 10014.0
The remainder is 107 after subtracting 2572 from 2679.
Bring next digit (9) of the dividend behind the 107 and repeat the process: 1079 / 643

Moving on to step 8:
If we divide 1079 by 643, we get 1 and a remainder of 436.
Put 1 as the next digit of the answer. 
Result so far: 100141.0
If we subtract 643 from 1079, we get 436.
Since there are no more digits in the dividend, we add a zero to the remainder making it 4360, and continue the process.

Advancing to step 9:
643 can be fit into 4360 6 times, resulting in a remainder of 502.
The next digit of our result is 6. 
Result so far: 100141.6
If we subtract 3858 from 4360, we get 502.
Since there are no more digits in the dividend, we add a zero to the remainder making it 5020, and continue the process.

On to step 10:
The number 643 fits into 5020 7 times, leaving a remainder of 519.
The number 7 becomes the next digit in our result. 
Result so far: 100141.67
Subtracting 4501 from 5020 leaves us with 519.
Since there are no more digits in the dividend, we add a zero to the remainder making it 5190, and continue the process.

Going ahead to step 11:
If we divide 5190 by 643, we get 8 and a remainder of 46.
The number 8 becomes the next digit in our result. 
Result so far: 100141.678
The remainder is 46 after subtracting 5144 from 5190.
Since there are no more digits in the dividend, we add a zero to the remainder making it 460, and continue the process.

Moving on to step 12:
If we divide 460 by 643, we get 0 and a remainder of 460.
Put 0 as the next digit of the answer. 
Result so far: 100141.678
If we subtract 0 from 460, we get 460.
Since there are no more digits in the dividend, we add a zero to the remainder making it 4600, and continue the process.

Moving on to step 13:
643 can be fit into 4600 7 times, resulting in a remainder of 99.
Put 7 as the next digit of the answer. 
Result so far: 100141.67807
If we subtract 4501 from 4600, we get 99.
Since there are no more digits in the dividend, we add a zero to the remainder making it 990, and continue the process.

On to step 14:
When dividing 990 by 643, we get 1 with a remainder of 347.
Put 1 as the next digit of the answer. 
Result so far: 100141.678071
Deduct 643 from 990 and we're left with 347.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3470, and continue the process.

Step 15:
When dividing 3470 by 643, we get 5 with a remainder of 255.
Put 5 as the next digit of the answer. 
Result so far: 100141.6780715
Subtracting 3215 from 3470 leaves us with 255.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2550, and continue the process.

Going ahead to step 16:
643 can be fit into 2550 3 times, resulting in a remainder of 621.
Put 3 as the next digit of the answer. 
Result so far: 100141.67807153
Subtract 1929 from 2550 to get 621.
Since there are no more digits in the dividend, we add a zero to the remainder making it 6210, and continue the process.

The quotient of the division is 100141.67807153, and the remainder is 6.21e-07.