We're dividing 405996 by 90 
The aim is to understand the frequency of 90 in 405996.

Going ahead to step 1:
90 can be fit into 4 0 times, resulting in a remainder of 4.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Subtract 0 from 4 to get 4.
Fetch the next digit (0) from the dividend, attach it to 4 and continue: 40 / 90

On to step 2:
The number 90 fits into 40 0 times, leaving a remainder of 40.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Subtracting 0 from 40 leaves us with 40.
Append the next digit (5) from the dividend to 40 and continue with: 405 / 90

Advancing to step 3:
When dividing 405 by 90, we get 4 with a remainder of 45.
The number 4 becomes the next digit in our result. 
Result so far: 4.0
Subtract 360 from 405 to get 45.
Include the next digit (9) from the dividend after 45, then repeat: 459 / 90

Advancing to step 4:
90 can be fit into 459 5 times, resulting in a remainder of 9.
Put 5 as the next digit of the answer. 
Result so far: 45.0
Deduct 450 from 459 and we're left with 9.
Bring next digit (9) of the dividend behind the 9 and repeat the process: 99 / 90

Advancing to step 5:
90 goes into 99 1 times with a remainder of 9.
Write down 1 as next digit of the result. 
Result so far: 451.0
If we take 90 away from 99, we end up with 9.
Grab the next digit (6) from the dividend, add it to 9, then carry on: 96 / 90

Advancing to step 6:
The number 90 fits into 96 1 times, leaving a remainder of 6.
The next digit of our result is 1. 
Result so far: 4511.0
Subtracting 90 from 96 leaves us with 6.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

On to step 7:
90 goes into 60 0 times with a remainder of 60.
The next digit of our result is 0. 
Result so far: 4511.0
If we subtract 0 from 60, we get 60.
Since there are no more digits in the dividend, we add a zero to the remainder making it 600, and continue the process.

Step 8:
90 goes into 600 6 times with a remainder of 60.
The number 6 becomes the next digit in our result. 
Result so far: 4511.06
Deduct 540 from 600 and we're left with 60.
Since there are no more digits in the dividend, we add a zero to the remainder making it 600, and continue the process.

Let's proceed to step 9:
90 can be fit into 600 6 times, resulting in a remainder of 60.
Write down 6 as next digit of the result. 
Result so far: 4511.066
Subtract 540 from 600 to get 60.
Since there are no more digits in the dividend, we add a zero to the remainder making it 600, and continue the process.

The final result is 4511.066 with a remainder of 0.006.