We look at the division of 83865983 by 645 
The aim is to understand the frequency of 645 in 83865983.

Moving on to step 1:
The number 645 fits into 8 0 times, leaving a remainder of 8.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
Subtracting 0 from 8 leaves us with 8.
Include the next digit (3) from the dividend after 8, then repeat: 83 / 645

Let's proceed to step 2:
If we divide 83 by 645, we get 0 and a remainder of 83.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
The remainder is 83 after subtracting 0 from 83.
Take the next digit (8) from the dividend and append it to 83, then repeat: 838 / 645

On to step 3:
The number 645 fits into 838 1 times, leaving a remainder of 193.
Write down 1 as next digit of the result. 
Result so far: 1.0
If we subtract 645 from 838, we get 193.
Take the next digit (6) from the dividend and append it to 193, then repeat: 1936 / 645

Let's proceed to step 4:
645 can be fit into 1936 3 times, resulting in a remainder of 1.
The number 3 becomes the next digit in our result. 
Result so far: 13.0
If we subtract 1935 from 1936, we get 1.
Grab the next digit (5) from the dividend, add it to 1, then carry on: 15 / 645

Moving on to step 5:
645 goes into 15 0 times with a remainder of 15.
The number 0 becomes the next digit in our result. 
Result so far: 130.0
The remainder is 15 after subtracting 0 from 15.
Grab the next digit (9) from the dividend, add it to 15, then carry on: 159 / 645

Moving on to step 6:
If we divide 159 by 645, we get 0 and a remainder of 159.
Use 0 as the next digit of our solution. 
Result so far: 1300.0
Deduct 0 from 159 and we're left with 159.
Grab the next digit (8) from the dividend, add it to 159, then carry on: 1598 / 645

Step 7:
When dividing 1598 by 645, we get 2 with a remainder of 308.
The number 2 becomes the next digit in our result. 
Result so far: 13002.0
Subtract 1290 from 1598 to get 308.
Append the next digit (3) from the dividend to 308 and continue with: 3083 / 645

Moving on to step 8:
The number 645 fits into 3083 4 times, leaving a remainder of 503.
Use 4 as the next digit of our solution. 
Result so far: 130024.0
The remainder is 503 after subtracting 2580 from 3083.
Since there are no more digits in the dividend, we add a zero to the remainder making it 5030, and continue the process.

Let's proceed to step 9:
645 can be fit into 5030 7 times, resulting in a remainder of 515.
Write down 7 as next digit of the result. 
Result so far: 130024.7
If we subtract 4515 from 5030, we get 515.
Since there are no more digits in the dividend, we add a zero to the remainder making it 5150, and continue the process.

Let's proceed to step 10:
If we divide 5150 by 645, we get 7 and a remainder of 635.
Record the quotient 7 as the next digit in the result. 
Result so far: 130024.77
If we take 4515 away from 5150, we end up with 635.
Since there are no more digits in the dividend, we add a zero to the remainder making it 6350, and continue the process.

The quotient of the division is 130024.77, and the remainder is 0.635.