We look at the division of 913374 by 21 
The aim is to understand the frequency of 21 in 913374.

On to step 1:
21 goes into 9 0 times with a remainder of 9.
Use 0 as the next digit of our solution. 
Result so far: 0.0
If we subtract 0 from 9, we get 9.
Fetch the next digit (1) from the dividend, attach it to 9 and continue: 91 / 21

Moving on to step 2:
The number 21 fits into 91 4 times, leaving a remainder of 7.
Record the quotient 4 as the next digit in the result. 
Result so far: 4.0
Subtracting 84 from 91 leaves us with 7.
Fetch the next digit (3) from the dividend, attach it to 7 and continue: 73 / 21

Step 3:
21 goes into 73 3 times with a remainder of 10.
The number 3 becomes the next digit in our result. 
Result so far: 43.0
Subtracting 63 from 73 leaves us with 10.
Append the next digit (3) from the dividend to 10 and continue with: 103 / 21

Going ahead to step 4:
If we divide 103 by 21, we get 4 and a remainder of 19.
The next digit of our result is 4. 
Result so far: 434.0
The remainder is 19 after subtracting 84 from 103.
Take the next digit (7) from the dividend and append it to 19, then repeat: 197 / 21

Moving on to step 5:
If we divide 197 by 21, we get 9 and a remainder of 8.
The number 9 becomes the next digit in our result. 
Result so far: 4349.0
If we subtract 189 from 197, we get 8.
Grab the next digit (4) from the dividend, add it to 8, then carry on: 84 / 21

Advancing to step 6:
The number 21 fits into 84 4 times, leaving a remainder of 0.
The number 4 becomes the next digit in our result. 
Result so far: 43494.0
If we take 84 away from 84, we end up 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.

Moving on to step 7:
If we divide 0 by 21, we get 0 and a remainder of 0.
Put 0 as the next digit of the answer. 
Result so far: 43494.0
If we subtract 0 from 0, we get 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

On to step 8:
The number 21 fits into 0 0 times, leaving a remainder of 0.
Put 0 as the next digit of the answer. 
Result so far: 43494.0
Subtract 0 from 0 to get 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 43494.0, with a leftover of 0.0.