We're dividing 807571 by 90 
The aim is to understand the frequency of 90 in 807571.

Step 1:
The number 90 fits into 8 0 times, leaving a remainder of 8.
Write down 0 as next digit of the result. 
Result so far: 0.0
If we take 0 away from 8, we end up with 8.
Include the next digit (0) from the dividend after 8, then repeat: 80 / 90

On to step 2:
90 goes into 80 0 times with a remainder of 80.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Deduct 0 from 80 and we're left with 80.
Include the next digit (7) from the dividend after 80, then repeat: 807 / 90

Step 3:
90 goes into 807 8 times with a remainder of 87.
The next digit of our result is 8. 
Result so far: 8.0
The remainder is 87 after subtracting 720 from 807.
Grab the next digit (5) from the dividend, add it to 87, then carry on: 875 / 90

Going ahead to step 4:
If we divide 875 by 90, we get 9 and a remainder of 65.
Use 9 as the next digit of our solution. 
Result so far: 89.0
Subtract 810 from 875 to get 65.
Append the next digit (7) from the dividend to 65 and continue with: 657 / 90

On to step 5:
90 goes into 657 7 times with a remainder of 27.
Put 7 as the next digit of the answer. 
Result so far: 897.0
If we take 630 away from 657, we end up with 27.
Include the next digit (1) from the dividend after 27, then repeat: 271 / 90

Moving on to step 6:
90 goes into 271 3 times with a remainder of 1.
The number 3 becomes the next digit in our result. 
Result so far: 8973.0
If we subtract 270 from 271, we get 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Advancing to step 7:
The number 90 fits into 10 0 times, leaving a remainder of 10.
Use 0 as the next digit of our solution. 
Result so far: 8973.0
If we take 0 away from 10, we end up with 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Moving on to step 8:
90 goes into 100 1 times with a remainder of 10.
The next digit of our result is 1. 
Result so far: 8973.01
If we subtract 90 from 100, we get 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

Going ahead to step 9:
If we divide 100 by 90, we get 1 and a remainder of 10.
The next digit of our result is 1. 
Result so far: 8973.011
Subtracting 90 from 100 leaves us with 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

After the division, we end up with 8973.011 and a remainder of 0.001.