We look at the division of 91428594 by 81 
The aim is to understand the frequency of 81 in 91428594.

On to step 1:
If we divide 9 by 81, we get 0 and a remainder of 9.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Deduct 0 from 9 and we're left with 9.
Include the next digit (1) from the dividend after 9, then repeat: 91 / 81

Advancing to step 2:
81 can be fit into 91 1 times, resulting in a remainder of 10.
Use 1 as the next digit of our solution. 
Result so far: 1.0
If we subtract 81 from 91, we get 10.
Fetch the next digit (4) from the dividend, attach it to 10 and continue: 104 / 81

Moving on to step 3:
81 goes into 104 1 times with a remainder of 23.
Write down 1 as next digit of the result. 
Result so far: 11.0
Subtracting 81 from 104 leaves us with 23.
Include the next digit (2) from the dividend after 23, then repeat: 232 / 81

Moving on to step 4:
232 divided by 81 is 2 with a remainder of 70.
Put 2 as the next digit of the answer. 
Result so far: 112.0
The remainder is 70 after subtracting 162 from 232.
Fetch the next digit (8) from the dividend, attach it to 70 and continue: 708 / 81

Going ahead to step 5:
81 goes into 708 8 times with a remainder of 60.
The number 8 becomes the next digit in our result. 
Result so far: 1128.0
Deduct 648 from 708 and we're left with 60.
Include the next digit (5) from the dividend after 60, then repeat: 605 / 81

Let's proceed to step 6:
81 can be fit into 605 7 times, resulting in a remainder of 38.
Record the quotient 7 as the next digit in the result. 
Result so far: 11287.0
The remainder is 38 after subtracting 567 from 605.
Fetch the next digit (9) from the dividend, attach it to 38 and continue: 389 / 81

Advancing to step 7:
389 divided by 81 is 4 with a remainder of 65.
The next digit of our result is 4. 
Result so far: 112874.0
Deduct 324 from 389 and we're left with 65.
Include the next digit (4) from the dividend after 65, then repeat: 654 / 81

On to step 8:
If we divide 654 by 81, we get 8 and a remainder of 6.
Use 8 as the next digit of our solution. 
Result so far: 1128748.0
If we take 648 away from 654, 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.

Moving on to step 9:
81 can be fit into 60 0 times, resulting in a remainder of 60.
The next digit of our result is 0. 
Result so far: 1128748.0
If we subtract 0 from 60, we get 60.
Since there are no more digits in the dividend, we add a zero to the remainder making it 600, and continue the process.

Moving on to step 10:
The number 81 fits into 600 7 times, leaving a remainder of 33.
The next digit of our result is 7. 
Result so far: 1128748.07
If we subtract 567 from 600, we get 33.
Since there are no more digits in the dividend, we add a zero to the remainder making it 330, and continue the process.

Going ahead to step 11:
When dividing 330 by 81, we get 4 with a remainder of 6.
Put 4 as the next digit of the answer. 
Result so far: 1128748.074
If we take 324 away from 330, 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.

Going ahead to step 12:
81 can be fit into 60 0 times, resulting in a remainder of 60.
Write down 0 as next digit of the result. 
Result so far: 1128748.074
If we take 0 away from 60, we end up with 60.
Since there are no more digits in the dividend, we add a zero to the remainder making it 600, and continue the process.

Step 13:
81 can be fit into 600 7 times, resulting in a remainder of 33.
The number 7 becomes the next digit in our result. 
Result so far: 1128748.07407
If we take 567 away from 600, we end up with 33.
Since there are no more digits in the dividend, we add a zero to the remainder making it 330, and continue the process.

Step 14:
330 divided by 81 is 4 with a remainder of 6.
The next digit of our result is 4. 
Result so far: 1128748.074074
Subtracting 324 from 330 leaves us 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.

Moving on to step 15:
81 goes into 60 0 times with a remainder of 60.
Write down 0 as next digit of the result. 
Result so far: 1128748.074074
If we take 0 away from 60, we end up with 60.
Since there are no more digits in the dividend, we add a zero to the remainder making it 600, and continue the process.

Moving on to step 16:
81 can be fit into 600 7 times, resulting in a remainder of 33.
Use 7 as the next digit of our solution. 
Result so far: 1128748.07407407
If we take 567 away from 600, we end up with 33.
Since there are no more digits in the dividend, we add a zero to the remainder making it 330, and continue the process.

Our division results in 1128748.07407407 with a remaining 3.3e-08.