75137866 ÷ 521 
The aim is to understand the frequency of 521 in 75137866.

Advancing to step 1:
7 divided by 521 is 0 with a remainder of 7.
The next digit of our result is 0. 
Result so far: 0.0
Subtract 0 from 7 to get 7.
Fetch the next digit (5) from the dividend, attach it to 7 and continue: 75 / 521

Going ahead to step 2:
521 can be fit into 75 0 times, resulting in a remainder of 75.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Deduct 0 from 75 and we're left with 75.
Include the next digit (1) from the dividend after 75, then repeat: 751 / 521

Advancing to step 3:
The number 521 fits into 751 1 times, leaving a remainder of 230.
Record the quotient 1 as the next digit in the result. 
Result so far: 1.0
If we take 521 away from 751, we end up with 230.
Include the next digit (3) from the dividend after 230, then repeat: 2303 / 521

Going ahead to step 4:
521 goes into 2303 4 times with a remainder of 219.
Put 4 as the next digit of the answer. 
Result so far: 14.0
If we subtract 2084 from 2303, we get 219.
Take the next digit (7) from the dividend and append it to 219, then repeat: 2197 / 521

On to step 5:
521 can be fit into 2197 4 times, resulting in a remainder of 113.
Record the quotient 4 as the next digit in the result. 
Result so far: 144.0
If we take 2084 away from 2197, we end up with 113.
Take the next digit (8) from the dividend and append it to 113, then repeat: 1138 / 521

On to step 6:
If we divide 1138 by 521, we get 2 and a remainder of 96.
Record the quotient 2 as the next digit in the result. 
Result so far: 1442.0
Deduct 1042 from 1138 and we're left with 96.
Append the next digit (6) from the dividend to 96 and continue with: 966 / 521

Let's proceed to step 7:
966 divided by 521 is 1 with a remainder of 445.
Write down 1 as next digit of the result. 
Result so far: 14421.0
If we take 521 away from 966, we end up with 445.
Bring next digit (6) of the dividend behind the 445 and repeat the process: 4456 / 521

On to step 8:
4456 divided by 521 is 8 with a remainder of 288.
Put 8 as the next digit of the answer. 
Result so far: 144218.0
Subtract 4168 from 4456 to get 288.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2880, and continue the process.

Let's proceed to step 9:
521 goes into 2880 5 times with a remainder of 275.
The number 5 becomes the next digit in our result. 
Result so far: 144218.5
The remainder is 275 after subtracting 2605 from 2880.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2750, and continue the process.

Step 10:
521 can be fit into 2750 5 times, resulting in a remainder of 145.
The number 5 becomes the next digit in our result. 
Result so far: 144218.55
Subtracting 2605 from 2750 leaves us with 145.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1450, and continue the process.

The final result is 144218.55 with a remainder of 0.145.