54457815 ÷ 90 
The aim is to understand the frequency of 90 in 54457815.

On to step 1:
If we divide 5 by 90, we get 0 and a remainder of 5.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Deduct 0 from 5 and we're left with 5.
Append the next digit (4) from the dividend to 5 and continue with: 54 / 90

Going ahead to step 2:
90 can be fit into 54 0 times, resulting in a remainder of 54.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
If we take 0 away from 54, we end up with 54.
Include the next digit (4) from the dividend after 54, then repeat: 544 / 90

Let's proceed to step 3:
When dividing 544 by 90, we get 6 with a remainder of 4.
Write down 6 as next digit of the result. 
Result so far: 6.0
Deduct 540 from 544 and we're left with 4.
Include the next digit (5) from the dividend after 4, then repeat: 45 / 90

Advancing to step 4:
The number 90 fits into 45 0 times, leaving a remainder of 45.
Put 0 as the next digit of the answer. 
Result so far: 60.0
Subtract 0 from 45 to get 45.
Bring next digit (7) of the dividend behind the 45 and repeat the process: 457 / 90

Moving on to step 5:
When dividing 457 by 90, we get 5 with a remainder of 7.
Use 5 as the next digit of our solution. 
Result so far: 605.0
If we subtract 450 from 457, we get 7.
Append the next digit (8) from the dividend to 7 and continue with: 78 / 90

Going ahead to step 6:
78 divided by 90 is 0 with a remainder of 78.
The number 0 becomes the next digit in our result. 
Result so far: 6050.0
If we take 0 away from 78, we end up with 78.
Bring next digit (1) of the dividend behind the 78 and repeat the process: 781 / 90

Going ahead to step 7:
781 divided by 90 is 8 with a remainder of 61.
Put 8 as the next digit of the answer. 
Result so far: 60508.0
The remainder is 61 after subtracting 720 from 781.
Bring next digit (5) of the dividend behind the 61 and repeat the process: 615 / 90

On to step 8:
615 divided by 90 is 6 with a remainder of 75.
Use 6 as the next digit of our solution. 
Result so far: 605086.0
If we subtract 540 from 615, we get 75.
Since there are no more digits in the dividend, we add a zero to the remainder making it 750, and continue the process.

Step 9:
90 can be fit into 750 8 times, resulting in a remainder of 30.
The number 8 becomes the next digit in our result. 
Result so far: 605086.8
If we subtract 720 from 750, we get 30.
Since there are no more digits in the dividend, we add a zero to the remainder making it 300, and continue the process.

Step 10:
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: 605086.83
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.

Step 11:
The number 90 fits into 300 3 times, leaving a remainder of 30.
Record the quotient 3 as the next digit in the result. 
Result so far: 605086.833
Subtract 270 from 300 to get 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 605086.833, with a leftover of 0.003.