We look at the division of 786072 by 21 
The aim is to understand the frequency of 21 in 786072.

Moving on to step 1:
If we divide 7 by 21, we get 0 and a remainder of 7.
Write down 0 as next digit of the result. 
Result so far: 0.0
The remainder is 7 after subtracting 0 from 7.
Include the next digit (8) from the dividend after 7, then repeat: 78 / 21

Step 2:
If we divide 78 by 21, we get 3 and a remainder of 15.
Put 3 as the next digit of the answer. 
Result so far: 3.0
The remainder is 15 after subtracting 63 from 78.
Take the next digit (6) from the dividend and append it to 15, then repeat: 156 / 21

Let's proceed to step 3:
The number 21 fits into 156 7 times, leaving a remainder of 9.
Write down 7 as next digit of the result. 
Result so far: 37.0
Subtract 147 from 156 to get 9.
Bring next digit (0) of the dividend behind the 9 and repeat the process: 90 / 21

On to step 4:
The number 21 fits into 90 4 times, leaving a remainder of 6.
The number 4 becomes the next digit in our result. 
Result so far: 374.0
Subtracting 84 from 90 leaves us with 6.
Append the next digit (7) from the dividend to 6 and continue with: 67 / 21

Going ahead to step 5:
If we divide 67 by 21, we get 3 and a remainder of 4.
The next digit of our result is 3. 
Result so far: 3743.0
Subtracting 63 from 67 leaves us with 4.
Grab the next digit (2) from the dividend, add it to 4, then carry on: 42 / 21

Advancing to step 6:
21 can be fit into 42 2 times, resulting in a remainder of 0.
The next digit of our result is 2. 
Result so far: 37432.0
Subtracting 42 from 42 leaves us with 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

Step 7:
The number 21 fits into 0 0 times, leaving a remainder of 0.
The number 0 becomes the next digit in our result. 
Result so far: 37432.0
Subtracting 0 from 0 leaves us with 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

Step 8:
21 can be fit into 0 0 times, resulting in a remainder of 0.
The number 0 becomes the next digit in our result. 
Result so far: 37432.0
Deduct 0 from 0 and we're left with 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

The final outcome is 37432.0, with a leftover of 0.0.