We're dividing 88621 by 21 
The aim is to understand the frequency of 21 in 88621.

On to step 1:
The number 21 fits into 8 0 times, leaving a remainder of 8.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
Deduct 0 from 8 and we're left with 8.
Take the next digit (8) from the dividend and append it to 8, then repeat: 88 / 21

Step 2:
If we divide 88 by 21, we get 4 and a remainder of 4.
Use 4 as the next digit of our solution. 
Result so far: 4.0
Subtract 84 from 88 to get 4.
Grab the next digit (6) from the dividend, add it to 4, then carry on: 46 / 21

Moving on to step 3:
If we divide 46 by 21, we get 2 and a remainder of 4.
The number 2 becomes the next digit in our result. 
Result so far: 42.0
Subtract 42 from 46 to get 4.
Grab the next digit (2) from the dividend, add it to 4, then carry on: 42 / 21

Step 4:
The number 21 fits into 42 2 times, leaving a remainder of 0.
Record the quotient 2 as the next digit in the result. 
Result so far: 422.0
Subtract 42 from 42 to get 0.
Include the next digit (1) from the dividend after 0, then repeat: 1 / 21

Advancing to step 5:
The number 21 fits into 1 0 times, leaving a remainder of 1.
The next digit of our result is 0. 
Result so far: 4220.0
If we subtract 0 from 1, we get 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Advancing to step 6:
If we divide 10 by 21, we get 0 and a remainder of 10.
Put 0 as the next digit of the answer. 
Result so far: 4220.0
Subtracting 0 from 10 leaves us with 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Going ahead to step 7:
The number 21 fits into 100 4 times, leaving a remainder of 16.
The next digit of our result is 4. 
Result so far: 4220.04
The remainder is 16 after subtracting 84 from 100.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

Let's proceed to step 8:
The number 21 fits into 160 7 times, leaving a remainder of 13.
Put 7 as the next digit of the answer. 
Result so far: 4220.047
If we take 147 away from 160, we end up with 13.
Since there are no more digits in the dividend, we add a zero to the remainder making it 130, and continue the process.

Step 9:
130 divided by 21 is 6 with a remainder of 4.
Put 6 as the next digit of the answer. 
Result so far: 4220.0476
Deduct 126 from 130 and we're left with 4.
Since there are no more digits in the dividend, we add a zero to the remainder making it 40, and continue the process.

Let's proceed to step 10:
If we divide 40 by 21, we get 1 and a remainder of 19.
The number 1 becomes the next digit in our result. 
Result so far: 4220.04761
Subtracting 21 from 40 leaves us with 19.
Since there are no more digits in the dividend, we add a zero to the remainder making it 190, and continue the process.

Step 11:
The number 21 fits into 190 9 times, leaving a remainder of 1.
Record the quotient 9 as the next digit in the result. 
Result so far: 4220.047619
If we take 189 away from 190, we end up with 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Let's proceed to step 12:
21 goes into 10 0 times with a remainder of 10.
Use 0 as the next digit of our solution. 
Result so far: 4220.047619
Subtracting 0 from 10 leaves us with 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Step 13:
The number 21 fits into 100 4 times, leaving a remainder of 16.
Use 4 as the next digit of our solution. 
Result so far: 4220.04761904
If we take 84 away from 100, we end up with 16.
Since there are no more digits in the dividend, we add a zero to the remainder making it 160, and continue the process.

The final result is 4220.04761904 with a remainder of 1.6e-08.