407521 divided by 90 
The aim is to understand the frequency of 90 in 407521.

On to step 1:
When dividing 4 by 90, we get 0 with a remainder of 4.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
Subtracting 0 from 4 leaves us with 4.
Include the next digit (0) from the dividend after 4, then repeat: 40 / 90

Let's proceed to step 2:
If we divide 40 by 90, we get 0 and a remainder of 40.
Write down 0 as next digit of the result. 
Result so far: 0.0
If we subtract 0 from 40, we get 40.
Grab the next digit (7) from the dividend, add it to 40, then carry on: 407 / 90

On to step 3:
407 divided by 90 is 4 with a remainder of 47.
Write down 4 as next digit of the result. 
Result so far: 4.0
Deduct 360 from 407 and we're left with 47.
Take the next digit (5) from the dividend and append it to 47, then repeat: 475 / 90

Let's proceed to step 4:
90 can be fit into 475 5 times, resulting in a remainder of 25.
Write down 5 as next digit of the result. 
Result so far: 45.0
Subtracting 450 from 475 leaves us with 25.
Include the next digit (2) from the dividend after 25, then repeat: 252 / 90

Advancing to step 5:
90 goes into 252 2 times with a remainder of 72.
Record the quotient 2 as the next digit in the result. 
Result so far: 452.0
If we subtract 180 from 252, we get 72.
Include the next digit (1) from the dividend after 72, then repeat: 721 / 90

Let's proceed to step 6:
When dividing 721 by 90, we get 8 with a remainder of 1.
Use 8 as the next digit of our solution. 
Result so far: 4528.0
Subtracting 720 from 721 leaves us with 1.
Since there are no more digits in the dividend, we add a zero to the remainder making it 10, and continue the process.

Step 7:
90 goes into 10 0 times with a remainder of 10.
The next digit of our result is 0. 
Result so far: 4528.0
Deduct 0 from 10 and we're left 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.

Advancing to step 8:
90 goes into 100 1 times with a remainder of 10.
Put 1 as the next digit of the answer. 
Result so far: 4528.01
If we take 90 away from 100, 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.

On to step 9:
If we divide 100 by 90, we get 1 and a remainder of 10.
The number 1 becomes the next digit in our result. 
Result so far: 4528.011
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.

Our division results in 4528.011 with a remaining 0.001.