We're dividing 908607 by 21 
The aim is to understand the frequency of 21 in 908607.

Step 1:
The number 21 fits into 9 0 times, leaving a remainder of 9.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Deduct 0 from 9 and we're left with 9.
Fetch the next digit (0) from the dividend, attach it to 9 and continue: 90 / 21

Advancing to step 2:
21 goes into 90 4 times with a remainder of 6.
Record the quotient 4 as the next digit in the result. 
Result so far: 4.0
If we take 84 away from 90, we end up with 6.
Include the next digit (8) from the dividend after 6, then repeat: 68 / 21

On to step 3:
When dividing 68 by 21, we get 3 with a remainder of 5.
The next digit of our result is 3. 
Result so far: 43.0
Subtract 63 from 68 to get 5.
Grab the next digit (6) from the dividend, add it to 5, then carry on: 56 / 21

Advancing to step 4:
When dividing 56 by 21, we get 2 with a remainder of 14.
Record the quotient 2 as the next digit in the result. 
Result so far: 432.0
The remainder is 14 after subtracting 42 from 56.
Take the next digit (0) from the dividend and append it to 14, then repeat: 140 / 21

Step 5:
The number 21 fits into 140 6 times, leaving a remainder of 14.
The number 6 becomes the next digit in our result. 
Result so far: 4326.0
If we subtract 126 from 140, we get 14.
Include the next digit (7) from the dividend after 14, then repeat: 147 / 21

Step 6:
If we divide 147 by 21, we get 7 and a remainder of 0.
Use 7 as the next digit of our solution. 
Result so far: 43267.0
The remainder is 0 after subtracting 147 from 147.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

Moving on to step 7:
When dividing 0 by 21, we get 0 with a remainder of 0.
The number 0 becomes the next digit in our result. 
Result so far: 43267.0
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.

Going ahead to step 8:
When dividing 0 by 21, we get 0 with a remainder of 0.
Write down 0 as next digit of the result. 
Result so far: 43267.0
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 43267.0, with a leftover of 0.0.