We look at the division of 388957 by 90 
The aim is to understand the frequency of 90 in 388957.

Let's proceed to step 1:
The number 90 fits into 3 0 times, leaving a remainder of 3.
Write down 0 as next digit of the result. 
Result so far: 0.0
If we subtract 0 from 3, we get 3.
Append the next digit (8) from the dividend to 3 and continue with: 38 / 90

Let's proceed to step 2:
90 can be fit into 38 0 times, resulting in a remainder of 38.
The next digit of our result is 0. 
Result so far: 0.0
The remainder is 38 after subtracting 0 from 38.
Grab the next digit (8) from the dividend, add it to 38, then carry on: 388 / 90

Step 3:
If we divide 388 by 90, we get 4 and a remainder of 28.
Put 4 as the next digit of the answer. 
Result so far: 4.0
If we take 360 away from 388, we end up with 28.
Include the next digit (9) from the dividend after 28, then repeat: 289 / 90

Going ahead to step 4:
If we divide 289 by 90, we get 3 and a remainder of 19.
The next digit of our result is 3. 
Result so far: 43.0
If we take 270 away from 289, we end up with 19.
Bring next digit (5) of the dividend behind the 19 and repeat the process: 195 / 90

Step 5:
The number 90 fits into 195 2 times, leaving a remainder of 15.
The number 2 becomes the next digit in our result. 
Result so far: 432.0
Subtracting 180 from 195 leaves us with 15.
Fetch the next digit (7) from the dividend, attach it to 15 and continue: 157 / 90

Step 6:
90 goes into 157 1 times with a remainder of 67.
Record the quotient 1 as the next digit in the result. 
Result so far: 4321.0
Subtracting 90 from 157 leaves us with 67.
Since there are no more digits in the dividend, we add a zero to the remainder making it 670, and continue the process.

Moving on to step 7:
If we divide 670 by 90, we get 7 and a remainder of 40.
The number 7 becomes the next digit in our result. 
Result so far: 4321.7
If we take 630 away from 670, we end up 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.

Moving on to step 8:
400 divided by 90 is 4 with a remainder of 40.
Use 4 as the next digit of our solution. 
Result so far: 4321.74
Deduct 360 from 400 and we're left 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.

Let's proceed to step 9:
90 goes into 400 4 times with a remainder of 40.
The number 4 becomes the next digit in our result. 
Result so far: 4321.744
The remainder is 40 after subtracting 360 from 400.
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 result is 4321.744 with a remainder of 0.004.