We look at the division of 3958 by 91 
The aim is to understand the frequency of 91 in 3958.

Let's proceed to step 1:
If we divide 3 by 91, we get 0 and a remainder of 3.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
The remainder is 3 after subtracting 0 from 3.
Append the next digit (9) from the dividend to 3 and continue with: 39 / 91

Step 2:
When dividing 39 by 91, we get 0 with a remainder of 39.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Subtracting 0 from 39 leaves us with 39.
Append the next digit (5) from the dividend to 39 and continue with: 395 / 91

Step 3:
91 goes into 395 4 times with a remainder of 31.
The next digit of our result is 4. 
Result so far: 4.0
Deduct 364 from 395 and we're left with 31.
Append the next digit (8) from the dividend to 31 and continue with: 318 / 91

Moving on to step 4:
318 divided by 91 is 3 with a remainder of 45.
The next digit of our result is 3. 
Result so far: 43.0
The remainder is 45 after subtracting 273 from 318.
Since there are no more digits in the dividend, we add a zero to the remainder making it 450, and continue the process.

Let's proceed to step 5:
450 divided by 91 is 4 with a remainder of 86.
The number 4 becomes the next digit in our result. 
Result so far: 43.4
Deduct 364 from 450 and we're left with 86.
Since there are no more digits in the dividend, we add a zero to the remainder making it 860, and continue the process.

Going ahead to step 6:
The number 91 fits into 860 9 times, leaving a remainder of 41.
Put 9 as the next digit of the answer. 
Result so far: 43.49
If we subtract 819 from 860, we get 41.
Since there are no more digits in the dividend, we add a zero to the remainder making it 410, and continue the process.

Let's proceed to step 7:
The number 91 fits into 410 4 times, leaving a remainder of 46.
Use 4 as the next digit of our solution. 
Result so far: 43.494
Deduct 364 from 410 and we're left with 46.
Since there are no more digits in the dividend, we add a zero to the remainder making it 460, and continue the process.

Moving on to step 8:
When dividing 460 by 91, we get 5 with a remainder of 5.
Put 5 as the next digit of the answer. 
Result so far: 43.4945
If we subtract 455 from 460, we get 5.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Let's proceed to step 9:
The number 91 fits into 50 0 times, leaving a remainder of 50.
Put 0 as the next digit of the answer. 
Result so far: 43.4945
Subtracting 0 from 50 leaves us with 50.
Since there are no more digits in the dividend, we add a zero to the remainder making it 500, and continue the process.

Advancing to step 10:
If we divide 500 by 91, we get 5 and a remainder of 45.
Write down 5 as next digit of the result. 
Result so far: 43.494505
Deduct 455 from 500 and we're left with 45.
Since there are no more digits in the dividend, we add a zero to the remainder making it 450, and continue the process.

Step 11:
The number 91 fits into 450 4 times, leaving a remainder of 86.
Use 4 as the next digit of our solution. 
Result so far: 43.4945054
Subtracting 364 from 450 leaves us with 86.
Since there are no more digits in the dividend, we add a zero to the remainder making it 860, and continue the process.

Step 12:
91 can be fit into 860 9 times, resulting in a remainder of 41.
Record the quotient 9 as the next digit in the result. 
Result so far: 43.49450549
If we take 819 away from 860, we end up with 41.
Since there are no more digits in the dividend, we add a zero to the remainder making it 410, and continue the process.

The final result is 43.49450549 with a remainder of 4.1e-08.