28724 divided by 21 
The aim is to understand the frequency of 21 in 28724.

On to step 1:
2 divided by 21 is 0 with a remainder of 2.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
If we take 0 away from 2, we end up with 2.
Append the next digit (8) from the dividend to 2 and continue with: 28 / 21

Let's proceed to step 2:
21 can be fit into 28 1 times, resulting in a remainder of 7.
The next digit of our result is 1. 
Result so far: 1.0
Deduct 21 from 28 and we're left with 7.
Include the next digit (7) from the dividend after 7, then repeat: 77 / 21

Let's proceed to step 3:
21 can be fit into 77 3 times, resulting in a remainder of 14.
The number 3 becomes the next digit in our result. 
Result so far: 13.0
If we take 63 away from 77, we end up with 14.
Take the next digit (2) from the dividend and append it to 14, then repeat: 142 / 21

On to step 4:
If we divide 142 by 21, we get 6 and a remainder of 16.
Put 6 as the next digit of the answer. 
Result so far: 136.0
If we subtract 126 from 142, we get 16.
Take the next digit (4) from the dividend and append it to 16, then repeat: 164 / 21

On to step 5:
If we divide 164 by 21, we get 7 and a remainder of 17.
Use 7 as the next digit of our solution. 
Result so far: 1367.0
Subtracting 147 from 164 leaves us with 17.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

Going ahead to step 6:
When dividing 170 by 21, we get 8 with a remainder of 2.
Use 8 as the next digit of our solution. 
Result so far: 1367.8
Subtract 168 from 170 to get 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:
20 divided by 21 is 0 with a remainder of 20.
Put 0 as the next digit of the answer. 
Result so far: 1367.8
The remainder is 20 after subtracting 0 from 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Advancing to step 8:
200 divided by 21 is 9 with a remainder of 11.
Put 9 as the next digit of the answer. 
Result so far: 1367.809
Deduct 189 from 200 and we're left with 11.
Since there are no more digits in the dividend, we add a zero to the remainder making it 110, and continue the process.

Let's proceed to step 9:
110 divided by 21 is 5 with a remainder of 5.
Put 5 as the next digit of the answer. 
Result so far: 1367.8095
Deduct 105 from 110 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.

Moving on to step 10:
When dividing 50 by 21, we get 2 with a remainder of 8.
Record the quotient 2 as the next digit in the result. 
Result so far: 1367.80952
The remainder is 8 after subtracting 42 from 50.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Advancing to step 11:
The number 21 fits into 80 3 times, leaving a remainder of 17.
Write down 3 as next digit of the result. 
Result so far: 1367.809523
Deduct 63 from 80 and we're left with 17.
Since there are no more digits in the dividend, we add a zero to the remainder making it 170, and continue the process.

On to step 12:
When dividing 170 by 21, we get 8 with a remainder of 2.
Put 8 as the next digit of the answer. 
Result so far: 1367.8095238
If we take 168 away from 170, we end up 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.

Advancing to step 13:
20 divided by 21 is 0 with a remainder of 20.
Record the quotient 0 as the next digit in the result. 
Result so far: 1367.8095238
The remainder is 20 after subtracting 0 from 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

After the division, we end up with 1367.8095238 and a remainder of 2e-08.