We look at the division of 12571990 by 642 
Let's see how many times 642 fits into 12571990.

On to step 1:
642 can be fit into 1 0 times, resulting in a remainder of 1.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
If we take 0 away from 1, we end up with 1.
Append the next digit (2) from the dividend to 1 and continue with: 12 / 642

Step 2:
642 can be fit into 12 0 times, resulting in a remainder of 12.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
Subtracting 0 from 12 leaves us with 12.
Fetch the next digit (5) from the dividend, attach it to 12 and continue: 125 / 642

Let's proceed to step 3:
The number 642 fits into 125 0 times, leaving a remainder of 125.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
Deduct 0 from 125 and we're left with 125.
Bring next digit (7) of the dividend behind the 125 and repeat the process: 1257 / 642

On to step 4:
If we divide 1257 by 642, we get 1 and a remainder of 615.
Write down 1 as next digit of the result. 
Result so far: 1.0
The remainder is 615 after subtracting 642 from 1257.
Bring next digit (1) of the dividend behind the 615 and repeat the process: 6151 / 642

Let's proceed to step 5:
642 goes into 6151 9 times with a remainder of 373.
Write down 9 as next digit of the result. 
Result so far: 19.0
If we subtract 5778 from 6151, we get 373.
Include the next digit (9) from the dividend after 373, then repeat: 3739 / 642

Advancing to step 6:
642 goes into 3739 5 times with a remainder of 529.
Record the quotient 5 as the next digit in the result. 
Result so far: 195.0
Subtract 3210 from 3739 to get 529.
Fetch the next digit (9) from the dividend, attach it to 529 and continue: 5299 / 642

Step 7:
If we divide 5299 by 642, we get 8 and a remainder of 163.
Write down 8 as next digit of the result. 
Result so far: 1958.0
If we take 5136 away from 5299, we end up with 163.
Include the next digit (0) from the dividend after 163, then repeat: 1630 / 642

Going ahead to step 8:
1630 divided by 642 is 2 with a remainder of 346.
Record the quotient 2 as the next digit in the result. 
Result so far: 19582.0
Subtracting 1284 from 1630 leaves us with 346.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3460, and continue the process.

Let's proceed to step 9:
642 can be fit into 3460 5 times, resulting in a remainder of 250.
The next digit of our result is 5. 
Result so far: 19582.5
Deduct 3210 from 3460 and we're left with 250.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2500, and continue the process.

Step 10:
If we divide 2500 by 642, we get 3 and a remainder of 574.
Use 3 as the next digit of our solution. 
Result so far: 19582.53
Subtract 1926 from 2500 to get 574.
Since there are no more digits in the dividend, we add a zero to the remainder making it 5740, and continue the process.

Step 11:
When dividing 5740 by 642, we get 8 with a remainder of 604.
The next digit of our result is 8. 
Result so far: 19582.538
If we take 5136 away from 5740, we end up with 604.
Since there are no more digits in the dividend, we add a zero to the remainder making it 6040, and continue the process.

Step 12:
If we divide 6040 by 642, we get 9 and a remainder of 262.
Use 9 as the next digit of our solution. 
Result so far: 19582.5389
If we subtract 5778 from 6040, we get 262.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2620, and continue the process.

Step 13:
When dividing 2620 by 642, we get 4 with a remainder of 52.
Record the quotient 4 as the next digit in the result. 
Result so far: 19582.53894
Deduct 2568 from 2620 and we're left with 52.
Since there are no more digits in the dividend, we add a zero to the remainder making it 520, and continue the process.

Step 14:
The number 642 fits into 520 0 times, leaving a remainder of 520.
Put 0 as the next digit of the answer. 
Result so far: 19582.53894
Subtract 0 from 520 to get 520.
Since there are no more digits in the dividend, we add a zero to the remainder making it 5200, and continue the process.

Advancing to step 15:
When dividing 5200 by 642, we get 8 with a remainder of 64.
Record the quotient 8 as the next digit in the result. 
Result so far: 19582.5389408
Subtract 5136 from 5200 to get 64.
Since there are no more digits in the dividend, we add a zero to the remainder making it 640, and continue the process.

Going ahead to step 16:
If we divide 640 by 642, we get 0 and a remainder of 640.
Put 0 as the next digit of the answer. 
Result so far: 19582.5389408
Subtracting 0 from 640 leaves us with 640.
Since there are no more digits in the dividend, we add a zero to the remainder making it 6400, and continue the process.

The final result is 19582.5389408 with a remainder of 6.4e-07.