We look at the division of 21551715 by 54 
The aim is to understand the frequency of 54 in 21551715.

Advancing to step 1:
When dividing 2 by 54, we get 0 with a remainder of 2.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
If we subtract 0 from 2, we get 2.
Bring next digit (1) of the dividend behind the 2 and repeat the process: 21 / 54

Let's proceed to step 2:
21 divided by 54 is 0 with a remainder of 21.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Subtracting 0 from 21 leaves us with 21.
Include the next digit (5) from the dividend after 21, then repeat: 215 / 54

Step 3:
54 can be fit into 215 3 times, resulting in a remainder of 53.
Use 3 as the next digit of our solution. 
Result so far: 3.0
Subtract 162 from 215 to get 53.
Bring next digit (5) of the dividend behind the 53 and repeat the process: 535 / 54

Moving on to step 4:
54 goes into 535 9 times with a remainder of 49.
The next digit of our result is 9. 
Result so far: 39.0
Subtract 486 from 535 to get 49.
Include the next digit (1) from the dividend after 49, then repeat: 491 / 54

Advancing to step 5:
When dividing 491 by 54, we get 9 with a remainder of 5.
The next digit of our result is 9. 
Result so far: 399.0
If we take 486 away from 491, we end up with 5.
Grab the next digit (7) from the dividend, add it to 5, then carry on: 57 / 54

Let's proceed to step 6:
54 can be fit into 57 1 times, resulting in a remainder of 3.
The number 1 becomes the next digit in our result. 
Result so far: 3991.0
Subtracting 54 from 57 leaves us with 3.
Bring next digit (1) of the dividend behind the 3 and repeat the process: 31 / 54

On to step 7:
31 divided by 54 is 0 with a remainder of 31.
Put 0 as the next digit of the answer. 
Result so far: 39910.0
Subtracting 0 from 31 leaves us with 31.
Bring next digit (5) of the dividend behind the 31 and repeat the process: 315 / 54

Going ahead to step 8:
If we divide 315 by 54, we get 5 and a remainder of 45.
Put 5 as the next digit of the answer. 
Result so far: 399105.0
If we subtract 270 from 315, we get 45.
Since there are no more digits in the dividend, we add a zero to the remainder making it 450, and continue the process.

Let's proceed to step 9:
54 goes into 450 8 times with a remainder of 18.
Write down 8 as next digit of the result. 
Result so far: 399105.8
Subtract 432 from 450 to get 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Let's proceed to step 10:
If we divide 180 by 54, we get 3 and a remainder of 18.
Write down 3 as next digit of the result. 
Result so far: 399105.83
Subtract 162 from 180 to get 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

Advancing to step 11:
180 divided by 54 is 3 with a remainder of 18.
Record the quotient 3 as the next digit in the result. 
Result so far: 399105.833
If we take 162 away from 180, we end up with 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

The final outcome is 399105.833, with a leftover of 0.0018.