We look at the division of 54150045 by 399 
The aim is to understand the frequency of 399 in 54150045.

Let's proceed to step 1:
5 divided by 399 is 0 with a remainder of 5.
The next digit of our result is 0. 
Result so far: 0.0
If we subtract 0 from 5, we get 5.
Append the next digit (4) from the dividend to 5 and continue with: 54 / 399

Advancing to step 2:
The number 399 fits into 54 0 times, leaving a remainder of 54.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
Subtracting 0 from 54 leaves us with 54.
Take the next digit (1) from the dividend and append it to 54, then repeat: 541 / 399

Let's proceed to step 3:
399 can be fit into 541 1 times, resulting in a remainder of 142.
The next digit of our result is 1. 
Result so far: 1.0
If we take 399 away from 541, we end up with 142.
Append the next digit (5) from the dividend to 142 and continue with: 1425 / 399

Advancing to step 4:
If we divide 1425 by 399, we get 3 and a remainder of 228.
Put 3 as the next digit of the answer. 
Result so far: 13.0
Deduct 1197 from 1425 and we're left with 228.
Bring next digit (0) of the dividend behind the 228 and repeat the process: 2280 / 399

Step 5:
2280 divided by 399 is 5 with a remainder of 285.
Write down 5 as next digit of the result. 
Result so far: 135.0
Subtracting 1995 from 2280 leaves us with 285.
Fetch the next digit (0) from the dividend, attach it to 285 and continue: 2850 / 399

On to step 6:
399 can be fit into 2850 7 times, resulting in a remainder of 57.
Use 7 as the next digit of our solution. 
Result so far: 1357.0
If we subtract 2793 from 2850, we get 57.
Fetch the next digit (4) from the dividend, attach it to 57 and continue: 574 / 399

Step 7:
399 can be fit into 574 1 times, resulting in a remainder of 175.
Write down 1 as next digit of the result. 
Result so far: 13571.0
Deduct 399 from 574 and we're left with 175.
Take the next digit (5) from the dividend and append it to 175, then repeat: 1755 / 399

Moving on to step 8:
When dividing 1755 by 399, we get 4 with a remainder of 159.
Write down 4 as next digit of the result. 
Result so far: 135714.0
Deduct 1596 from 1755 and we're left with 159.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1590, and continue the process.

Going ahead to step 9:
When dividing 1590 by 399, we get 3 with a remainder of 393.
Use 3 as the next digit of our solution. 
Result so far: 135714.3
If we subtract 1197 from 1590, we get 393.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3930, and continue the process.

On to step 10:
If we divide 3930 by 399, we get 9 and a remainder of 339.
Use 9 as the next digit of our solution. 
Result so far: 135714.39
If we subtract 3591 from 3930, we get 339.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3390, and continue the process.

Let's proceed to step 11:
3390 divided by 399 is 8 with a remainder of 198.
Use 8 as the next digit of our solution. 
Result so far: 135714.398
If we take 3192 away from 3390, we end up with 198.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1980, and continue the process.

Advancing to step 12:
1980 divided by 399 is 4 with a remainder of 384.
The number 4 becomes the next digit in our result. 
Result so far: 135714.3984
Deduct 1596 from 1980 and we're left with 384.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3840, and continue the process.

Step 13:
If we divide 3840 by 399, we get 9 and a remainder of 249.
Use 9 as the next digit of our solution. 
Result so far: 135714.39849
The remainder is 249 after subtracting 3591 from 3840.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2490, and continue the process.

On to step 14:
2490 divided by 399 is 6 with a remainder of 96.
Record the quotient 6 as the next digit in the result. 
Result so far: 135714.398496
Subtracting 2394 from 2490 leaves us with 96.
Since there are no more digits in the dividend, we add a zero to the remainder making it 960, and continue the process.

On to step 15:
If we divide 960 by 399, we get 2 and a remainder of 162.
The next digit of our result is 2. 
Result so far: 135714.3984962
If we take 798 away from 960, we end up with 162.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1620, and continue the process.

Going ahead to step 16:
If we divide 1620 by 399, we get 4 and a remainder of 24.
The next digit of our result is 4. 
Result so far: 135714.39849624
Subtracting 1596 from 1620 leaves us with 24.
Since there are no more digits in the dividend, we add a zero to the remainder making it 240, and continue the process.

The final outcome is 135714.39849624, with a leftover of 2.4e-08.