We're dividing 51578576 by 409 
The aim is to understand the frequency of 409 in 51578576.

On to step 1:
The number 409 fits into 5 0 times, leaving a remainder of 5.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
If we subtract 0 from 5, we get 5.
Append the next digit (1) from the dividend to 5 and continue with: 51 / 409

On to step 2:
When dividing 51 by 409, we get 0 with a remainder of 51.
Put 0 as the next digit of the answer. 
Result so far: 0.0
If we subtract 0 from 51, we get 51.
Append the next digit (5) from the dividend to 51 and continue with: 515 / 409

Step 3:
The number 409 fits into 515 1 times, leaving a remainder of 106.
Use 1 as the next digit of our solution. 
Result so far: 1.0
Subtracting 409 from 515 leaves us with 106.
Bring next digit (7) of the dividend behind the 106 and repeat the process: 1067 / 409

Advancing to step 4:
409 can be fit into 1067 2 times, resulting in a remainder of 249.
Write down 2 as next digit of the result. 
Result so far: 12.0
Subtract 818 from 1067 to get 249.
Append the next digit (8) from the dividend to 249 and continue with: 2498 / 409

Step 5:
When dividing 2498 by 409, we get 6 with a remainder of 44.
Put 6 as the next digit of the answer. 
Result so far: 126.0
If we subtract 2454 from 2498, we get 44.
Take the next digit (5) from the dividend and append it to 44, then repeat: 445 / 409

Going ahead to step 6:
409 can be fit into 445 1 times, resulting in a remainder of 36.
The number 1 becomes the next digit in our result. 
Result so far: 1261.0
If we subtract 409 from 445, we get 36.
Bring next digit (7) of the dividend behind the 36 and repeat the process: 367 / 409

Step 7:
367 divided by 409 is 0 with a remainder of 367.
Use 0 as the next digit of our solution. 
Result so far: 12610.0
Subtract 0 from 367 to get 367.
Take the next digit (6) from the dividend and append it to 367, then repeat: 3676 / 409

On to step 8:
The number 409 fits into 3676 8 times, leaving a remainder of 404.
Put 8 as the next digit of the answer. 
Result so far: 126108.0
If we take 3272 away from 3676, we end up with 404.
Since there are no more digits in the dividend, we add a zero to the remainder making it 4040, and continue the process.

Moving on to step 9:
409 can be fit into 4040 9 times, resulting in a remainder of 359.
The next digit of our result is 9. 
Result so far: 126108.9
Deduct 3681 from 4040 and we're left with 359.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3590, and continue the process.

Going ahead to step 10:
If we divide 3590 by 409, we get 8 and a remainder of 318.
Put 8 as the next digit of the answer. 
Result so far: 126108.98
Deduct 3272 from 3590 and we're left with 318.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3180, and continue the process.

Let's proceed to step 11:
The number 409 fits into 3180 7 times, leaving a remainder of 317.
The number 7 becomes the next digit in our result. 
Result so far: 126108.987
The remainder is 317 after subtracting 2863 from 3180.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3170, and continue the process.

Advancing to step 12:
If we divide 3170 by 409, we get 7 and a remainder of 307.
The number 7 becomes the next digit in our result. 
Result so far: 126108.9877
If we subtract 2863 from 3170, we get 307.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3070, and continue the process.

The final result is 126108.9877 with a remainder of 0.00307.