We're dividing 3990543 by 643 
We want to figure out the number of times 3990543 can be divided by 643.

Let's proceed to step 1:
3 divided by 643 is 0 with a remainder of 3.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
If we subtract 0 from 3, we get 3.
Append the next digit (9) from the dividend to 3 and continue with: 39 / 643

Step 2:
When dividing 39 by 643, we get 0 with a remainder of 39.
The next digit of our result is 0. 
Result so far: 0.0
If we subtract 0 from 39, we get 39.
Fetch the next digit (9) from the dividend, attach it to 39 and continue: 399 / 643

Step 3:
The number 643 fits into 399 0 times, leaving a remainder of 399.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
Deduct 0 from 399 and we're left with 399.
Append the next digit (0) from the dividend to 399 and continue with: 3990 / 643

Let's proceed to step 4:
643 can be fit into 3990 6 times, resulting in a remainder of 132.
Write down 6 as next digit of the result. 
Result so far: 6.0
Subtract 3858 from 3990 to get 132.
Grab the next digit (5) from the dividend, add it to 132, then carry on: 1325 / 643

Going ahead to step 5:
When dividing 1325 by 643, we get 2 with a remainder of 39.
Write down 2 as next digit of the result. 
Result so far: 62.0
The remainder is 39 after subtracting 1286 from 1325.
Take the next digit (4) from the dividend and append it to 39, then repeat: 394 / 643

Advancing to step 6:
The number 643 fits into 394 0 times, leaving a remainder of 394.
Put 0 as the next digit of the answer. 
Result so far: 620.0
Deduct 0 from 394 and we're left with 394.
Grab the next digit (3) from the dividend, add it to 394, then carry on: 3943 / 643

Step 7:
3943 divided by 643 is 6 with a remainder of 85.
Record the quotient 6 as the next digit in the result. 
Result so far: 6206.0
The remainder is 85 after subtracting 3858 from 3943.
Since there are no more digits in the dividend, we add a zero to the remainder making it 850, and continue the process.

Advancing to step 8:
When dividing 850 by 643, we get 1 with a remainder of 207.
Use 1 as the next digit of our solution. 
Result so far: 6206.1
Deduct 643 from 850 and we're left with 207.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2070, and continue the process.

Going ahead to step 9:
When dividing 2070 by 643, we get 3 with a remainder of 141.
Write down 3 as next digit of the result. 
Result so far: 6206.13
If we subtract 1929 from 2070, we get 141.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1410, and continue the process.

Moving on to step 10:
1410 divided by 643 is 2 with a remainder of 124.
Record the quotient 2 as the next digit in the result. 
Result so far: 6206.132
Subtracting 1286 from 1410 leaves us with 124.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1240, and continue the process.

Let's proceed to step 11:
If we divide 1240 by 643, we get 1 and a remainder of 597.
Put 1 as the next digit of the answer. 
Result so far: 6206.1321
Subtract 643 from 1240 to get 597.
Since there are no more digits in the dividend, we add a zero to the remainder making it 5970, and continue the process.

On to step 12:
When dividing 5970 by 643, we get 9 with a remainder of 183.
Record the quotient 9 as the next digit in the result. 
Result so far: 6206.13219
Deduct 5787 from 5970 and we're left with 183.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1830, and continue the process.

Step 13:
The number 643 fits into 1830 2 times, leaving a remainder of 544.
Record the quotient 2 as the next digit in the result. 
Result so far: 6206.132192
Subtract 1286 from 1830 to get 544.
Since there are no more digits in the dividend, we add a zero to the remainder making it 5440, and continue the process.

On to step 14:
643 can be fit into 5440 8 times, resulting in a remainder of 296.
Write down 8 as next digit of the result. 
Result so far: 6206.1321928
If we subtract 5144 from 5440, we get 296.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2960, and continue the process.

Let's proceed to step 15:
2960 divided by 643 is 4 with a remainder of 388.
Use 4 as the next digit of our solution. 
Result so far: 6206.13219284
Subtract 2572 from 2960 to get 388.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3880, and continue the process.

The final outcome is 6206.13219284, with a leftover of 3.88e-07.