We're dividing 129207 by 21 
We want to figure out the number of times 129207 can be divided by 21.

On to step 1:
If we divide 1 by 21, we get 0 and 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.
Grab the next digit (2) from the dividend, add it to 1, then carry on: 12 / 21

Let's proceed to step 2:
The number 21 fits into 12 0 times, leaving a remainder of 12.
The next digit of our result is 0. 
Result so far: 0.0
Subtracting 0 from 12 leaves us with 12.
Append the next digit (9) from the dividend to 12 and continue with: 129 / 21

Let's proceed to step 3:
21 can be fit into 129 6 times, resulting in a remainder of 3.
Put 6 as the next digit of the answer. 
Result so far: 6.0
Deduct 126 from 129 and we're left with 3.
Grab the next digit (2) from the dividend, add it to 3, then carry on: 32 / 21

Going ahead to step 4:
If we divide 32 by 21, we get 1 and a remainder of 11.
Use 1 as the next digit of our solution. 
Result so far: 61.0
Subtract 21 from 32 to get 11.
Append the next digit (0) from the dividend to 11 and continue with: 110 / 21

Let's proceed to step 5:
21 goes into 110 5 times with a remainder of 5.
The next digit of our result is 5. 
Result so far: 615.0
The remainder is 5 after subtracting 105 from 110.
Take the next digit (7) from the dividend and append it to 5, then repeat: 57 / 21

Let's proceed to step 6:
When dividing 57 by 21, we get 2 with a remainder of 15.
Write down 2 as next digit of the result. 
Result so far: 6152.0
Subtracting 42 from 57 leaves us with 15.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

On to step 7:
150 divided by 21 is 7 with a remainder of 3.
Write down 7 as next digit of the result. 
Result so far: 6152.7
The remainder is 3 after subtracting 147 from 150.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Step 8:
If we divide 30 by 21, we get 1 and a remainder of 9.
Use 1 as the next digit of our solution. 
Result so far: 6152.71
Deduct 21 from 30 and we're left with 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

Let's proceed to step 9:
21 can be fit into 90 4 times, resulting in a remainder of 6.
Use 4 as the next digit of our solution. 
Result so far: 6152.714
If we subtract 84 from 90, we get 6.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

Going ahead to step 10:
When dividing 60 by 21, we get 2 with a remainder of 18.
The next digit of our result is 2. 
Result so far: 6152.7142
Deduct 42 from 60 and we're left with 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Let's proceed to step 11:
180 divided by 21 is 8 with a remainder of 12.
Record the quotient 8 as the next digit in the result. 
Result so far: 6152.71428
Deduct 168 from 180 and we're left with 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

Advancing to step 12:
If we divide 120 by 21, we get 5 and a remainder of 15.
The number 5 becomes the next digit in our result. 
Result so far: 6152.714285
The remainder is 15 after subtracting 105 from 120.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

Moving on to step 13:
The number 21 fits into 150 7 times, leaving a remainder of 3.
Put 7 as the next digit of the answer. 
Result so far: 6152.7142857
If we take 147 away from 150, we end up with 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Step 14:
21 goes into 30 1 times with a remainder of 9.
The number 1 becomes the next digit in our result. 
Result so far: 6152.71428571
If we take 21 away from 30, we end up with 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

The final outcome is 6152.71428571, with a leftover of 9e-09.