58250789 ÷ 399 
The aim is to understand the frequency of 399 in 58250789.

Going ahead to step 1:
When dividing 5 by 399, we get 0 with a remainder of 5.
The next digit of our result is 0. 
Result so far: 0.0
Subtract 0 from 5 to get 5.
Take the next digit (8) from the dividend and append it to 5, then repeat: 58 / 399

On to step 2:
58 divided by 399 is 0 with a remainder of 58.
Write down 0 as next digit of the result. 
Result so far: 0.0
Deduct 0 from 58 and we're left with 58.
Take the next digit (2) from the dividend and append it to 58, then repeat: 582 / 399

Step 3:
When dividing 582 by 399, we get 1 with a remainder of 183.
Use 1 as the next digit of our solution. 
Result so far: 1.0
Subtract 399 from 582 to get 183.
Append the next digit (5) from the dividend to 183 and continue with: 1835 / 399

Advancing to step 4:
399 goes into 1835 4 times with a remainder of 239.
Write down 4 as next digit of the result. 
Result so far: 14.0
The remainder is 239 after subtracting 1596 from 1835.
Fetch the next digit (0) from the dividend, attach it to 239 and continue: 2390 / 399

Let's proceed to step 5:
399 goes into 2390 5 times with a remainder of 395.
Write down 5 as next digit of the result. 
Result so far: 145.0
The remainder is 395 after subtracting 1995 from 2390.
Grab the next digit (7) from the dividend, add it to 395, then carry on: 3957 / 399

Advancing to step 6:
399 goes into 3957 9 times with a remainder of 366.
The next digit of our result is 9. 
Result so far: 1459.0
The remainder is 366 after subtracting 3591 from 3957.
Fetch the next digit (8) from the dividend, attach it to 366 and continue: 3668 / 399

Let's proceed to step 7:
399 can be fit into 3668 9 times, resulting in a remainder of 77.
Write down 9 as next digit of the result. 
Result so far: 14599.0
Deduct 3591 from 3668 and we're left with 77.
Append the next digit (9) from the dividend to 77 and continue with: 779 / 399

Advancing to step 8:
399 goes into 779 1 times with a remainder of 380.
The next digit of our result is 1. 
Result so far: 145991.0
Subtract 399 from 779 to get 380.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3800, and continue the process.

Advancing to step 9:
When dividing 3800 by 399, we get 9 with a remainder of 209.
Record the quotient 9 as the next digit in the result. 
Result so far: 145991.9
If we take 3591 away from 3800, we end up with 209.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2090, and continue the process.

Moving on to step 10:
The number 399 fits into 2090 5 times, leaving a remainder of 95.
Write down 5 as next digit of the result. 
Result so far: 145991.95
Subtracting 1995 from 2090 leaves us with 95.
Since there are no more digits in the dividend, we add a zero to the remainder making it 950, and continue the process.

Advancing to step 11:
When dividing 950 by 399, we get 2 with a remainder of 152.
Use 2 as the next digit of our solution. 
Result so far: 145991.952
Subtracting 798 from 950 leaves us with 152.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1520, and continue the process.

Going ahead to step 12:
1520 divided by 399 is 3 with a remainder of 323.
Put 3 as the next digit of the answer. 
Result so far: 145991.9523
Subtracting 1197 from 1520 leaves us with 323.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3230, and continue the process.

Let's proceed to step 13:
399 goes into 3230 8 times with a remainder of 38.
The next digit of our result is 8. 
Result so far: 145991.95238
Subtracting 3192 from 3230 leaves us with 38.
Since there are no more digits in the dividend, we add a zero to the remainder making it 380, and continue the process.

Going ahead to step 14:
380 divided by 399 is 0 with a remainder of 380.
Write down 0 as next digit of the result. 
Result so far: 145991.95238
Subtracting 0 from 380 leaves us with 380.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3800, and continue the process.

On to step 15:
The number 399 fits into 3800 9 times, leaving a remainder of 209.
The number 9 becomes the next digit in our result. 
Result so far: 145991.9523809
The remainder is 209 after subtracting 3591 from 3800.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2090, and continue the process.

Let's proceed to step 16:
When dividing 2090 by 399, we get 5 with a remainder of 95.
Put 5 as the next digit of the answer. 
Result so far: 145991.95238095
Deduct 1995 from 2090 and we're left with 95.
Since there are no more digits in the dividend, we add a zero to the remainder making it 950, and continue the process.

The final outcome is 145991.95238095, with a leftover of 9.5e-08.