We look at the division of 40521 by 90 
We want to figure out the number of times 40521 can be divided by 90.

Step 1:
When dividing 4 by 90, we get 0 with a remainder of 4.
Write down 0 as next digit of the result. 
Result so far: 0.0
Deduct 0 from 4 and we're left with 4.
Include the next digit (0) from the dividend after 4, then repeat: 40 / 90

Going ahead to step 2:
90 goes into 40 0 times with a remainder of 40.
Use 0 as the next digit of our solution. 
Result so far: 0.0
Subtract 0 from 40 to get 40.
Grab the next digit (5) from the dividend, add it to 40, then carry on: 405 / 90

Advancing to step 3:
90 goes into 405 4 times with a remainder of 45.
Record the quotient 4 as the next digit in the result. 
Result so far: 4.0
Subtract 360 from 405 to get 45.
Take the next digit (2) from the dividend and append it to 45, then repeat: 452 / 90

On to step 4:
The number 90 fits into 452 5 times, leaving a remainder of 2.
The number 5 becomes the next digit in our result. 
Result so far: 45.0
Subtract 450 from 452 to get 2.
Include the next digit (1) from the dividend after 2, then repeat: 21 / 90

Advancing to step 5:
When dividing 21 by 90, we get 0 with a remainder of 21.
Use 0 as the next digit of our solution. 
Result so far: 450.0
The remainder is 21 after subtracting 0 from 21.
Since there are no more digits in the dividend, we add a zero to the remainder making it 210, and continue the process.

Let's proceed to step 6:
When dividing 210 by 90, we get 2 with a remainder of 30.
Record the quotient 2 as the next digit in the result. 
Result so far: 450.2
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.

Moving on to step 7:
90 goes into 300 3 times with a remainder of 30.
The number 3 becomes the next digit in our result. 
Result so far: 450.23
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.

Let's proceed to step 8:
When dividing 300 by 90, we get 3 with a remainder of 30.
Record the quotient 3 as the next digit in the result. 
Result so far: 450.233
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 450.233, with a leftover of 0.003.