399315 ÷ 81 
The aim is to understand the frequency of 81 in 399315.

Step 1:
When dividing 3 by 81, we get 0 with a remainder of 3.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
The remainder is 3 after subtracting 0 from 3.
Grab the next digit (9) from the dividend, add it to 3, then carry on: 39 / 81

Moving on to step 2:
39 divided by 81 is 0 with a remainder of 39.
Use 0 as the next digit of our solution. 
Result so far: 0.0
If we subtract 0 from 39, we get 39.
Fetch the next digit (9) from the dividend, attach it to 39 and continue: 399 / 81

On to step 3:
81 can be fit into 399 4 times, resulting in a remainder of 75.
Write down 4 as next digit of the result. 
Result so far: 4.0
If we subtract 324 from 399, we get 75.
Fetch the next digit (3) from the dividend, attach it to 75 and continue: 753 / 81

Moving on to step 4:
If we divide 753 by 81, we get 9 and a remainder of 24.
The next digit of our result is 9. 
Result so far: 49.0
Deduct 729 from 753 and we're left with 24.
Include the next digit (1) from the dividend after 24, then repeat: 241 / 81

Step 5:
The number 81 fits into 241 2 times, leaving a remainder of 79.
The next digit of our result is 2. 
Result so far: 492.0
If we take 162 away from 241, we end up with 79.
Include the next digit (5) from the dividend after 79, then repeat: 795 / 81

Going ahead to step 6:
81 can be fit into 795 9 times, resulting in a remainder of 66.
Record the quotient 9 as the next digit in the result. 
Result so far: 4929.0
Deduct 729 from 795 and we're left with 66.
Since there are no more digits in the dividend, we add a zero to the remainder making it 660, and continue the process.

Advancing to step 7:
81 goes into 660 8 times with a remainder of 12.
Record the quotient 8 as the next digit in the result. 
Result so far: 4929.8
Subtract 648 from 660 to get 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

Going ahead to step 8:
If we divide 120 by 81, we get 1 and a remainder of 39.
The next digit of our result is 1. 
Result so far: 4929.81
If we take 81 away from 120, we end up 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.

Advancing to step 9:
81 goes into 390 4 times with a remainder of 66.
Use 4 as the next digit of our solution. 
Result so far: 4929.814
If we subtract 324 from 390, we get 66.
Since there are no more digits in the dividend, we add a zero to the remainder making it 660, and continue the process.

Moving on to step 10:
660 divided by 81 is 8 with a remainder of 12.
The number 8 becomes the next digit in our result. 
Result so far: 4929.8148
The remainder is 12 after subtracting 648 from 660.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

Advancing to step 11:
If we divide 120 by 81, we get 1 and a remainder of 39.
Use 1 as the next digit of our solution. 
Result so far: 4929.81481
Deduct 81 from 120 and we're left 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.

Let's proceed to step 12:
If we divide 390 by 81, we get 4 and a remainder of 66.
Use 4 as the next digit of our solution. 
Result so far: 4929.814814
The remainder is 66 after subtracting 324 from 390.
Since there are no more digits in the dividend, we add a zero to the remainder making it 660, and continue the process.

Moving on to step 13:
If we divide 660 by 81, we get 8 and a remainder of 12.
Use 8 as the next digit of our solution. 
Result so far: 4929.8148148
Deduct 648 from 660 and we're left with 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

On to step 14:
120 divided by 81 is 1 with a remainder of 39.
Put 1 as the next digit of the answer. 
Result so far: 4929.81481481
Subtract 81 from 120 to get 39.
Since there are no more digits in the dividend, we add a zero to the remainder making it 390, and continue the process.

After the division, we end up with 4929.81481481 and a remainder of 3.9e-08.