We look at the division of 205851 by 90 
The aim is to understand the frequency of 90 in 205851.

On to step 1:
When dividing 2 by 90, we get 0 with a remainder of 2.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
If we take 0 away from 2, we end up with 2.
Grab the next digit (0) from the dividend, add it to 2, then carry on: 20 / 90

Let's proceed to step 2:
If we divide 20 by 90, we get 0 and a remainder of 20.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Subtract 0 from 20 to get 20.
Take the next digit (5) from the dividend and append it to 20, then repeat: 205 / 90

Step 3:
205 divided by 90 is 2 with a remainder of 25.
Write down 2 as next digit of the result. 
Result so far: 2.0
The remainder is 25 after subtracting 180 from 205.
Take the next digit (8) from the dividend and append it to 25, then repeat: 258 / 90

On to step 4:
When dividing 258 by 90, we get 2 with a remainder of 78.
The number 2 becomes the next digit in our result. 
Result so far: 22.0
Deduct 180 from 258 and we're left with 78.
Include the next digit (5) from the dividend after 78, then repeat: 785 / 90

Going ahead to step 5:
90 can be fit into 785 8 times, resulting in a remainder of 65.
The next digit of our result is 8. 
Result so far: 228.0
If we take 720 away from 785, we end up with 65.
Include the next digit (1) from the dividend after 65, then repeat: 651 / 90

Let's proceed to step 6:
The number 90 fits into 651 7 times, leaving a remainder of 21.
Use 7 as the next digit of our solution. 
Result so far: 2287.0
Deduct 630 from 651 and we're left with 21.
Since there are no more digits in the dividend, we add a zero to the remainder making it 210, and continue the process.

On to step 7:
When dividing 210 by 90, we get 2 with a remainder of 30.
Write down 2 as next digit of the result. 
Result so far: 2287.2
The remainder is 30 after subtracting 180 from 210.
Since there are no more digits in the dividend, we add a zero to the remainder making it 300, and continue the process.

Step 8:
If we divide 300 by 90, we get 3 and a remainder of 30.
The next digit of our result is 3. 
Result so far: 2287.23
Deduct 270 from 300 and we're left with 30.
Since there are no more digits in the dividend, we add a zero to the remainder making it 300, and continue the process.

Advancing to step 9:
If we divide 300 by 90, we get 3 and a remainder of 30.
Record the quotient 3 as the next digit in the result. 
Result so far: 2287.233
If we take 270 away from 300, we end up with 30.
Since there are no more digits in the dividend, we add a zero to the remainder making it 300, and continue the process.

The final outcome is 2287.233, with a leftover of 0.003.