We divide 978909 by 21
The aim is to understand the frequency of 21 in 978909.

Moving on to step 1:
When dividing 9 by 21, we get 0 with a remainder of 9.
The next digit of our result is 0. 
Result so far: 0.0
If we subtract 0 from 9, we get 9.
Take the next digit (7) from the dividend and append it to 9, then repeat: 97 / 21

Going ahead to step 2:
If we divide 97 by 21, we get 4 and a remainder of 13.
Write down 4 as next digit of the result. 
Result so far: 4.0
Deduct 84 from 97 and we're left with 13.
Append the next digit (8) from the dividend to 13 and continue with: 138 / 21

Advancing to step 3:
21 goes into 138 6 times with a remainder of 12.
The next digit of our result is 6. 
Result so far: 46.0
If we take 126 away from 138, we end up with 12.
Fetch the next digit (9) from the dividend, attach it to 12 and continue: 129 / 21

Going ahead to step 4:
21 goes into 129 6 times with a remainder of 3.
Record the quotient 6 as the next digit in the result. 
Result so far: 466.0
Subtracting 126 from 129 leaves us with 3.
Fetch the next digit (0) from the dividend, attach it to 3 and continue: 30 / 21

On to step 5:
When dividing 30 by 21, we get 1 with a remainder of 9.
Write down 1 as next digit of the result. 
Result so far: 4661.0
Subtracting 21 from 30 leaves us with 9.
Take the next digit (9) from the dividend and append it to 9, then repeat: 99 / 21

Going ahead to step 6:
21 can be fit into 99 4 times, resulting in a remainder of 15.
The number 4 becomes the next digit in our result. 
Result so far: 46614.0
If we subtract 84 from 99, we get 15.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

Step 7:
The number 21 fits into 150 7 times, leaving a remainder of 3.
The next digit of our result is 7. 
Result so far: 46614.7
Subtracting 147 from 150 leaves us with 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Step 8:
The number 21 fits into 30 1 times, leaving a remainder of 9.
The next digit of our result is 1. 
Result so far: 46614.71
If we subtract 21 from 30, we get 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

On to step 9:
When dividing 90 by 21, we get 4 with a remainder of 6.
Put 4 as the next digit of the answer. 
Result so far: 46614.714
If we take 84 away from 90, we end up with 6.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

Step 10:
The number 21 fits into 60 2 times, leaving a remainder of 18.
Use 2 as the next digit of our solution. 
Result so far: 46614.7142
If we take 42 away from 60, we end up with 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Let's proceed to step 11:
If we divide 180 by 21, we get 8 and a remainder of 12.
The next digit of our result is 8. 
Result so far: 46614.71428
If we subtract 168 from 180, we get 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

Going ahead to step 12:
120 divided by 21 is 5 with a remainder of 15.
The number 5 becomes the next digit in our result. 
Result so far: 46614.714285
If we subtract 105 from 120, we get 15.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

On to step 13:
The number 21 fits into 150 7 times, leaving a remainder of 3.
Put 7 as the next digit of the answer. 
Result so far: 46614.7142857
Subtracting 147 from 150 leaves us with 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Moving on to step 14:
30 divided by 21 is 1 with a remainder of 9.
Write down 1 as next digit of the result. 
Result so far: 46614.71428571
Deduct 21 from 30 and we're left with 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

The final result is 46614.71428571 with a remainder of 9e-09.