We look at the division of 66921541 by 86 
The aim is to understand the frequency of 86 in 66921541.

Advancing to step 1:
The number 86 fits into 6 0 times, leaving a remainder of 6.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
Subtract 0 from 6 to get 6.
Fetch the next digit (6) from the dividend, attach it to 6 and continue: 66 / 86

Moving on to step 2:
When dividing 66 by 86, we get 0 with a remainder of 66.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
The remainder is 66 after subtracting 0 from 66.
Bring next digit (9) of the dividend behind the 66 and repeat the process: 669 / 86

On to step 3:
669 divided by 86 is 7 with a remainder of 67.
Record the quotient 7 as the next digit in the result. 
Result so far: 7.0
Subtracting 602 from 669 leaves us with 67.
Include the next digit (2) from the dividend after 67, then repeat: 672 / 86

Moving on to step 4:
When dividing 672 by 86, we get 7 with a remainder of 70.
Record the quotient 7 as the next digit in the result. 
Result so far: 77.0
If we subtract 602 from 672, we get 70.
Bring next digit (1) of the dividend behind the 70 and repeat the process: 701 / 86

Let's proceed to step 5:
86 goes into 701 8 times with a remainder of 13.
Put 8 as the next digit of the answer. 
Result so far: 778.0
Deduct 688 from 701 and we're left with 13.
Fetch the next digit (5) from the dividend, attach it to 13 and continue: 135 / 86

On to step 6:
86 goes into 135 1 times with a remainder of 49.
Put 1 as the next digit of the answer. 
Result so far: 7781.0
Subtracting 86 from 135 leaves us with 49.
Fetch the next digit (4) from the dividend, attach it to 49 and continue: 494 / 86

Advancing to step 7:
When dividing 494 by 86, we get 5 with a remainder of 64.
Put 5 as the next digit of the answer. 
Result so far: 77815.0
Subtracting 430 from 494 leaves us with 64.
Bring next digit (1) of the dividend behind the 64 and repeat the process: 641 / 86

Going ahead to step 8:
The number 86 fits into 641 7 times, leaving a remainder of 39.
Use 7 as the next digit of our solution. 
Result so far: 778157.0
Subtracting 602 from 641 leaves us with 39.
Since there are no more digits in the dividend, we add a zero to the remainder making it 390, and continue the process.

On to step 9:
390 divided by 86 is 4 with a remainder of 46.
Put 4 as the next digit of the answer. 
Result so far: 778157.4
Subtracting 344 from 390 leaves us 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.

On to step 10:
86 can be fit into 460 5 times, resulting in a remainder of 30.
The number 5 becomes the next digit in our result. 
Result so far: 778157.45
Deduct 430 from 460 and we're left with 30.
Since there are no more digits in the dividend, we add a zero to the remainder making it 300, and continue the process.

Advancing to step 11:
300 divided by 86 is 3 with a remainder of 42.
Use 3 as the next digit of our solution. 
Result so far: 778157.453
The remainder is 42 after subtracting 258 from 300.
Since there are no more digits in the dividend, we add a zero to the remainder making it 420, and continue the process.

On to step 12:
If we divide 420 by 86, we get 4 and a remainder of 76.
Put 4 as the next digit of the answer. 
Result so far: 778157.4534
If we subtract 344 from 420, we get 76.
Since there are no more digits in the dividend, we add a zero to the remainder making it 760, and continue the process.

On to step 13:
The number 86 fits into 760 8 times, leaving a remainder of 72.
Use 8 as the next digit of our solution. 
Result so far: 778157.45348
Subtract 688 from 760 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.

Advancing to step 14:
720 divided by 86 is 8 with a remainder of 32.
The number 8 becomes the next digit in our result. 
Result so far: 778157.453488
If we subtract 688 from 720, we get 32.
Since there are no more digits in the dividend, we add a zero to the remainder making it 320, and continue the process.

The final result is 778157.453488 with a remainder of 3.2e-06.