We look at the division of 72861815 by 645 
The aim is to understand the frequency of 645 in 72861815.

Moving on to step 1:
7 divided by 645 is 0 with a remainder of 7.
Write down 0 as next digit of the result. 
Result so far: 0.0
If we subtract 0 from 7, we get 7.
Take the next digit (2) from the dividend and append it to 7, then repeat: 72 / 645

Moving on to step 2:
When dividing 72 by 645, we get 0 with a remainder of 72.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Subtracting 0 from 72 leaves us with 72.
Append the next digit (8) from the dividend to 72 and continue with: 728 / 645

On to step 3:
If we divide 728 by 645, we get 1 and a remainder of 83.
Record the quotient 1 as the next digit in the result. 
Result so far: 1.0
Subtract 645 from 728 to get 83.
Grab the next digit (6) from the dividend, add it to 83, then carry on: 836 / 645

On to step 4:
The number 645 fits into 836 1 times, leaving a remainder of 191.
Record the quotient 1 as the next digit in the result. 
Result so far: 11.0
If we subtract 645 from 836, we get 191.
Append the next digit (1) from the dividend to 191 and continue with: 1911 / 645

On to step 5:
1911 divided by 645 is 2 with a remainder of 621.
Record the quotient 2 as the next digit in the result. 
Result so far: 112.0
If we take 1290 away from 1911, we end up with 621.
Bring next digit (8) of the dividend behind the 621 and repeat the process: 6218 / 645

Step 6:
When dividing 6218 by 645, we get 9 with a remainder of 413.
Use 9 as the next digit of our solution. 
Result so far: 1129.0
Subtract 5805 from 6218 to get 413.
Append the next digit (1) from the dividend to 413 and continue with: 4131 / 645

On to step 7:
When dividing 4131 by 645, we get 6 with a remainder of 261.
Record the quotient 6 as the next digit in the result. 
Result so far: 11296.0
If we subtract 3870 from 4131, we get 261.
Include the next digit (5) from the dividend after 261, then repeat: 2615 / 645

Let's proceed to step 8:
If we divide 2615 by 645, we get 4 and a remainder of 35.
The next digit of our result is 4. 
Result so far: 112964.0
If we take 2580 away from 2615, we end up with 35.
Since there are no more digits in the dividend, we add a zero to the remainder making it 350, and continue the process.

Moving on to step 9:
When dividing 350 by 645, we get 0 with a remainder of 350.
Use 0 as the next digit of our solution. 
Result so far: 112964.0
Subtract 0 from 350 to get 350.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3500, and continue the process.

Going ahead to step 10:
When dividing 3500 by 645, we get 5 with a remainder of 275.
The next digit of our result is 5. 
Result so far: 112964.05
The remainder is 275 after subtracting 3225 from 3500.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2750, and continue the process.

Moving on to step 11:
If we divide 2750 by 645, we get 4 and a remainder of 170.
The number 4 becomes the next digit in our result. 
Result so far: 112964.054
The remainder is 170 after subtracting 2580 from 2750.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1700, and continue the process.

Let's proceed to step 12:
If we divide 1700 by 645, we get 2 and a remainder of 410.
Put 2 as the next digit of the answer. 
Result so far: 112964.0542
Subtract 1290 from 1700 to get 410.
Since there are no more digits in the dividend, we add a zero to the remainder making it 4100, and continue the process.

Going ahead to step 13:
4100 divided by 645 is 6 with a remainder of 230.
Record the quotient 6 as the next digit in the result. 
Result so far: 112964.05426
If we take 3870 away from 4100, we end up with 230.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2300, and continue the process.

Moving on to step 14:
645 goes into 2300 3 times with a remainder of 365.
Write down 3 as next digit of the result. 
Result so far: 112964.054263
Subtract 1935 from 2300 to get 365.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3650, and continue the process.

Going ahead to step 15:
645 goes into 3650 5 times with a remainder of 425.
Put 5 as the next digit of the answer. 
Result so far: 112964.0542635
Deduct 3225 from 3650 and we're left with 425.
Since there are no more digits in the dividend, we add a zero to the remainder making it 4250, and continue the process.

Moving on to step 16:
645 can be fit into 4250 6 times, resulting in a remainder of 380.
The number 6 becomes the next digit in our result. 
Result so far: 112964.05426356
Subtract 3870 from 4250 to get 380.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3800, and continue the process.

After the division, we end up with 112964.05426356 and a remainder of 3.8e-07.