We're dividing 21209 by 12 
The aim is to understand the frequency of 12 in 21209.

Step 1:
When dividing 2 by 12, we get 0 with a remainder of 2.
The next digit of our result is 0. 
Result so far: 0.0
Deduct 0 from 2 and we're left with 2.
Grab the next digit (1) from the dividend, add it to 2, then carry on: 21 / 12

Let's proceed to step 2:
21 divided by 12 is 1 with a remainder of 9.
Use 1 as the next digit of our solution. 
Result so far: 1.0
The remainder is 9 after subtracting 12 from 21.
Append the next digit (2) from the dividend to 9 and continue with: 92 / 12

Advancing to step 3:
92 divided by 12 is 7 with a remainder of 8.
Use 7 as the next digit of our solution. 
Result so far: 17.0
The remainder is 8 after subtracting 84 from 92.
Bring next digit (0) of the dividend behind the 8 and repeat the process: 80 / 12

Moving on to step 4:
12 can be fit into 80 6 times, resulting in a remainder of 8.
Record the quotient 6 as the next digit in the result. 
Result so far: 176.0
If we take 72 away from 80, we end up with 8.
Append the next digit (9) from the dividend to 8 and continue with: 89 / 12

Moving on to step 5:
12 goes into 89 7 times with a remainder of 5.
Write down 7 as next digit of the result. 
Result so far: 1767.0
If we subtract 84 from 89, we get 5.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Advancing to step 6:
12 can be fit into 50 4 times, resulting in a remainder of 2.
The next digit of our result is 4. 
Result so far: 1767.4
Deduct 48 from 50 and we're left with 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

Moving on to step 7:
When dividing 20 by 12, we get 1 with a remainder of 8.
Put 1 as the next digit of the answer. 
Result so far: 1767.41
Deduct 12 from 20 and we're left with 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

On to step 8:
If we divide 80 by 12, we get 6 and a remainder of 8.
Use 6 as the next digit of our solution. 
Result so far: 1767.416
Subtracting 72 from 80 leaves us with 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Let's proceed to step 9:
12 goes into 80 6 times with a remainder of 8.
Use 6 as the next digit of our solution. 
Result so far: 1767.4166
If we take 72 away from 80, we end up with 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

After the division, we end up with 1767.4166 and a remainder of 8e-05.