Let's divide 121121 by 15
The aim is to understand the frequency of 15 in 121121.

Going ahead to step 1:
The number 15 fits into 1 0 times, leaving a remainder of 1.
Write down 0 as next digit of the result. 
Result so far: 0.0
Subtract 0 from 1 to get 1.
Take the next digit (2) from the dividend and append it to 1, then repeat: 12 / 15

Step 2:
The number 15 fits into 12 0 times, leaving 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.
Take the next digit (1) from the dividend and append it to 12, then repeat: 121 / 15

Step 3:
15 can be fit into 121 8 times, resulting in a remainder of 1.
Record the quotient 8 as the next digit in the result. 
Result so far: 8.0
The remainder is 1 after subtracting 120 from 121.
Grab the next digit (1) from the dividend, add it to 1, then carry on: 11 / 15

On to step 4:
15 can be fit into 11 0 times, resulting in a remainder of 11.
Put 0 as the next digit of the answer. 
Result so far: 80.0
The remainder is 11 after subtracting 0 from 11.
Append the next digit (2) from the dividend to 11 and continue with: 112 / 15

Going ahead to step 5:
When dividing 112 by 15, we get 7 with a remainder of 7.
The next digit of our result is 7. 
Result so far: 807.0
Subtracting 105 from 112 leaves us with 7.
Include the next digit (1) from the dividend after 7, then repeat: 71 / 15

Moving on to step 6:
15 can be fit into 71 4 times, resulting in a remainder of 11.
Use 4 as the next digit of our solution. 
Result so far: 8074.0
The remainder is 11 after subtracting 60 from 71.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

Advancing to step 7:
110 divided by 15 is 7 with a remainder of 5.
Use 7 as the next digit of our solution. 
Result so far: 8074.7
If we subtract 105 from 110, 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.

Going ahead to step 8:
The number 15 fits into 50 3 times, leaving a remainder of 5.
Record the quotient 3 as the next digit in the result. 
Result so far: 8074.73
If we take 45 away from 50, we end up with 5.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

On to step 9:
If we divide 50 by 15, we get 3 and a remainder of 5.
The next digit of our result is 3. 
Result so far: 8074.733
Deduct 45 from 50 and we're left with 5.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

The final result is 8074.733 with a remainder of 0.0005.