We look at the division of 401572 by 90 
The aim is to understand the frequency of 90 in 401572.

Moving on to step 1:
If we divide 4 by 90, we get 0 and a remainder of 4.
The next digit of our result is 0. 
Result so far: 0.0
The remainder is 4 after subtracting 0 from 4.
Append the next digit (0) from the dividend to 4 and continue with: 40 / 90

On to step 2:
90 can be fit into 40 0 times, resulting in a remainder of 40.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
If we take 0 away from 40, we end up with 40.
Grab the next digit (1) from the dividend, add it to 40, then carry on: 401 / 90

Moving on to step 3:
The number 90 fits into 401 4 times, leaving a remainder of 41.
Write down 4 as next digit of the result. 
Result so far: 4.0
The remainder is 41 after subtracting 360 from 401.
Take the next digit (5) from the dividend and append it to 41, then repeat: 415 / 90

Advancing to step 4:
The number 90 fits into 415 4 times, leaving a remainder of 55.
The number 4 becomes the next digit in our result. 
Result so far: 44.0
Deduct 360 from 415 and we're left with 55.
Append the next digit (7) from the dividend to 55 and continue with: 557 / 90

Advancing to step 5:
If we divide 557 by 90, we get 6 and a remainder of 17.
Record the quotient 6 as the next digit in the result. 
Result so far: 446.0
Subtracting 540 from 557 leaves us with 17.
Grab the next digit (2) from the dividend, add it to 17, then carry on: 172 / 90

Going ahead to step 6:
172 divided by 90 is 1 with a remainder of 82.
Record the quotient 1 as the next digit in the result. 
Result so far: 4461.0
If we subtract 90 from 172, we get 82.
Since there are no more digits in the dividend, we add a zero to the remainder making it 820, and continue the process.

On to step 7:
90 goes into 820 9 times with a remainder of 10.
The number 9 becomes the next digit in our result. 
Result so far: 4461.9
Subtract 810 from 820 to 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.

On to step 8:
90 can be fit into 100 1 times, resulting in a remainder of 10.
Use 1 as the next digit of our solution. 
Result so far: 4461.91
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.

Let's proceed to step 9:
90 goes into 100 1 times with a remainder of 10.
Put 1 as the next digit of the answer. 
Result so far: 4461.911
Subtract 90 from 100 to 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.

After the division, we end up with 4461.911 and a remainder of 0.001.