We look at the division of 638649 by 91 
The aim is to understand the frequency of 91 in 638649.

Moving on to step 1:
If we divide 6 by 91, we get 0 and a remainder of 6.
Write down 0 as next digit of the result. 
Result so far: 0.0
If we subtract 0 from 6, we get 6.
Fetch the next digit (3) from the dividend, attach it to 6 and continue: 63 / 91

Moving on to step 2:
If we divide 63 by 91, we get 0 and a remainder of 63.
The next digit of our result is 0. 
Result so far: 0.0
If we take 0 away from 63, we end up with 63.
Take the next digit (8) from the dividend and append it to 63, then repeat: 638 / 91

On to step 3:
When dividing 638 by 91, we get 7 with a remainder of 1.
The number 7 becomes the next digit in our result. 
Result so far: 7.0
Subtract 637 from 638 to get 1.
Bring next digit (6) of the dividend behind the 1 and repeat the process: 16 / 91

Advancing to step 4:
If we divide 16 by 91, we get 0 and a remainder of 16.
The next digit of our result is 0. 
Result so far: 70.0
Subtract 0 from 16 to get 16.
Include the next digit (4) from the dividend after 16, then repeat: 164 / 91

Step 5:
If we divide 164 by 91, we get 1 and a remainder of 73.
Use 1 as the next digit of our solution. 
Result so far: 701.0
If we take 91 away from 164, we end up with 73.
Append the next digit (9) from the dividend to 73 and continue with: 739 / 91

Advancing to step 6:
If we divide 739 by 91, we get 8 and a remainder of 11.
Record the quotient 8 as the next digit in the result. 
Result so far: 7018.0
If we take 728 away from 739, we end up 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 7:
110 divided by 91 is 1 with a remainder of 19.
The next digit of our result is 1. 
Result so far: 7018.1
If we take 91 away from 110, we end up 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.

Advancing to step 8:
190 divided by 91 is 2 with a remainder of 8.
The next digit of our result is 2. 
Result so far: 7018.12
The remainder is 8 after subtracting 182 from 190.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Step 9:
When dividing 80 by 91, we get 0 with a remainder of 80.
Put 0 as the next digit of the answer. 
Result so far: 7018.12
Subtracting 0 from 80 leaves us with 80.
Since there are no more digits in the dividend, we add a zero to the remainder making it 800, and continue the process.

On to step 10:
800 divided by 91 is 8 with a remainder of 72.
Put 8 as the next digit of the answer. 
Result so far: 7018.1208
Subtract 728 from 800 to get 72.
Since there are no more digits in the dividend, we add a zero to the remainder making it 720, and continue the process.

Moving on to step 11:
If we divide 720 by 91, we get 7 and a remainder of 83.
Put 7 as the next digit of the answer. 
Result so far: 7018.12087
Subtracting 637 from 720 leaves us with 83.
Since there are no more digits in the dividend, we add a zero to the remainder making it 830, and continue the process.

Moving on to step 12:
830 divided by 91 is 9 with a remainder of 11.
Write down 9 as next digit of the result. 
Result so far: 7018.120879
Subtracting 819 from 830 leaves us 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.

Going ahead to step 13:
When dividing 110 by 91, we get 1 with a remainder of 19.
Write down 1 as next digit of the result. 
Result so far: 7018.1208791
Deduct 91 from 110 and we're left 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.

Let's proceed to step 14:
91 goes into 190 2 times with a remainder of 8.
The number 2 becomes the next digit in our result. 
Result so far: 7018.12087912
Subtracting 182 from 190 leaves us with 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

The final result is 7018.12087912 with a remainder of 8e-09.