We look at the division of 645051 by 66 
The aim is to understand the frequency of 66 in 645051.

Advancing to step 1:
6 divided by 66 is 0 with a remainder of 6.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Subtract 0 from 6 to get 6.
Fetch the next digit (4) from the dividend, attach it to 6 and continue: 64 / 66

Let's proceed to step 2:
The number 66 fits into 64 0 times, leaving a remainder of 64.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
Subtract 0 from 64 to get 64.
Include the next digit (5) from the dividend after 64, then repeat: 645 / 66

Going ahead to step 3:
66 can be fit into 645 9 times, resulting in a remainder of 51.
Write down 9 as next digit of the result. 
Result so far: 9.0
Subtract 594 from 645 to get 51.
Append the next digit (0) from the dividend to 51 and continue with: 510 / 66

On to step 4:
The number 66 fits into 510 7 times, leaving a remainder of 48.
Write down 7 as next digit of the result. 
Result so far: 97.0
Deduct 462 from 510 and we're left with 48.
Include the next digit (5) from the dividend after 48, then repeat: 485 / 66

Advancing to step 5:
If we divide 485 by 66, we get 7 and a remainder of 23.
Record the quotient 7 as the next digit in the result. 
Result so far: 977.0
If we take 462 away from 485, we end up with 23.
Append the next digit (1) from the dividend to 23 and continue with: 231 / 66

Advancing to step 6:
66 goes into 231 3 times with a remainder of 33.
Use 3 as the next digit of our solution. 
Result so far: 9773.0
Subtracting 198 from 231 leaves us with 33.
Since there are no more digits in the dividend, we add a zero to the remainder making it 330, and continue the process.

Advancing to step 7:
When dividing 330 by 66, we get 5 with a remainder of 0.
The next digit of our result is 5. 
Result so far: 9773.5
Subtract 330 from 330 to get 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

Advancing to step 8:
0 divided by 66 is 0 with a remainder of 0.
The next digit of our result is 0. 
Result so far: 9773.5
Deduct 0 from 0 and we're left with 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

Advancing to step 9:
The number 66 fits into 0 0 times, leaving a remainder of 0.
Use 0 as the next digit of our solution. 
Result so far: 9773.5
If we take 0 away from 0, we end up with 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

The final result is 9773.5 with a remainder of 0.0.