We look at the division of 390775 by 90 
The aim is to understand the frequency of 90 in 390775.

Step 1:
90 goes into 3 0 times with a remainder of 3.
The next digit of our result is 0. 
Result so far: 0.0
Deduct 0 from 3 and we're left with 3.
Include the next digit (9) from the dividend after 3, then repeat: 39 / 90

Advancing to step 2:
The number 90 fits into 39 0 times, leaving a remainder of 39.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
Subtract 0 from 39 to get 39.
Grab the next digit (0) from the dividend, add it to 39, then carry on: 390 / 90

Step 3:
90 can be fit into 390 4 times, resulting in a remainder of 30.
Write down 4 as next digit of the result. 
Result so far: 4.0
Subtracting 360 from 390 leaves us with 30.
Append the next digit (7) from the dividend to 30 and continue with: 307 / 90

Step 4:
If we divide 307 by 90, we get 3 and a remainder of 37.
The next digit of our result is 3. 
Result so far: 43.0
If we subtract 270 from 307, we get 37.
Take the next digit (7) from the dividend and append it to 37, then repeat: 377 / 90

Let's proceed to step 5:
90 goes into 377 4 times with a remainder of 17.
Use 4 as the next digit of our solution. 
Result so far: 434.0
The remainder is 17 after subtracting 360 from 377.
Grab the next digit (5) from the dividend, add it to 17, then carry on: 175 / 90

Step 6:
If we divide 175 by 90, we get 1 and a remainder of 85.
Write down 1 as next digit of the result. 
Result so far: 4341.0
The remainder is 85 after subtracting 90 from 175.
Since there are no more digits in the dividend, we add a zero to the remainder making it 850, and continue the process.

Going ahead to step 7:
90 can be fit into 850 9 times, resulting in a remainder of 40.
The number 9 becomes the next digit in our result. 
Result so far: 4341.9
Subtracting 810 from 850 leaves us with 40.
Since there are no more digits in the dividend, we add a zero to the remainder making it 400, and continue the process.

Going ahead to step 8:
When dividing 400 by 90, we get 4 with a remainder of 40.
Put 4 as the next digit of the answer. 
Result so far: 4341.94
If we subtract 360 from 400, we get 40.
Since there are no more digits in the dividend, we add a zero to the remainder making it 400, and continue the process.

Advancing to step 9:
The number 90 fits into 400 4 times, leaving a remainder of 40.
The next digit of our result is 4. 
Result so far: 4341.944
Subtract 360 from 400 to get 40.
Since there are no more digits in the dividend, we add a zero to the remainder making it 400, and continue the process.

The final outcome is 4341.944, with a leftover of 0.004.