We're dividing 387428 by 90 
The aim is to understand the frequency of 90 in 387428.

Step 1:
When dividing 3 by 90, we get 0 with a remainder of 3.
The next digit of our result is 0. 
Result so far: 0.0
If we take 0 away from 3, we end up with 3.
Fetch the next digit (8) from the dividend, attach it to 3 and continue: 38 / 90

Moving on to step 2:
38 divided by 90 is 0 with a remainder of 38.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
Deduct 0 from 38 and we're left with 38.
Append the next digit (7) from the dividend to 38 and continue with: 387 / 90

Going ahead to step 3:
When dividing 387 by 90, we get 4 with a remainder of 27.
Put 4 as the next digit of the answer. 
Result so far: 4.0
Subtract 360 from 387 to get 27.
Grab the next digit (4) from the dividend, add it to 27, then carry on: 274 / 90

Advancing to step 4:
90 can be fit into 274 3 times, resulting in a remainder of 4.
The next digit of our result is 3. 
Result so far: 43.0
Subtract 270 from 274 to get 4.
Include the next digit (2) from the dividend after 4, then repeat: 42 / 90

Step 5:
If we divide 42 by 90, we get 0 and a remainder of 42.
Record the quotient 0 as the next digit in the result. 
Result so far: 430.0
Subtract 0 from 42 to get 42.
Include the next digit (8) from the dividend after 42, then repeat: 428 / 90

Step 6:
90 goes into 428 4 times with a remainder of 68.
Put 4 as the next digit of the answer. 
Result so far: 4304.0
Deduct 360 from 428 and we're left with 68.
Since there are no more digits in the dividend, we add a zero to the remainder making it 680, and continue the process.

Going ahead to step 7:
If we divide 680 by 90, we get 7 and a remainder of 50.
Use 7 as the next digit of our solution. 
Result so far: 4304.7
Deduct 630 from 680 and we're left with 50.
Since there are no more digits in the dividend, we add a zero to the remainder making it 500, and continue the process.

Going ahead to step 8:
90 can be fit into 500 5 times, resulting in a remainder of 50.
Write down 5 as next digit of the result. 
Result so far: 4304.75
Deduct 450 from 500 and we're left with 50.
Since there are no more digits in the dividend, we add a zero to the remainder making it 500, and continue the process.

Moving on to step 9:
500 divided by 90 is 5 with a remainder of 50.
Write down 5 as next digit of the result. 
Result so far: 4304.755
Subtract 450 from 500 to get 50.
Since there are no more digits in the dividend, we add a zero to the remainder making it 500, and continue the process.

The final result is 4304.755 with a remainder of 0.005.