We look at the division of 643872 by 64 
The aim is to understand the frequency of 64 in 643872.

On to step 1:
When dividing 6 by 64, we get 0 with a remainder of 6.
Put 0 as the next digit of the answer. 
Result so far: 0.0
If we subtract 0 from 6, we get 6.
Include the next digit (4) from the dividend after 6, then repeat: 64 / 64

Going ahead to step 2:
If we divide 64 by 64, we get 1 and a remainder of 0.
Record the quotient 1 as the next digit in the result. 
Result so far: 1.0
If we take 64 away from 64, we end up with 0.
Append the next digit (3) from the dividend to 0 and continue with: 3 / 64

Step 3:
64 goes into 3 0 times with a remainder of 3.
Record the quotient 0 as the next digit in the result. 
Result so far: 10.0
If we subtract 0 from 3, we get 3.
Append the next digit (8) from the dividend to 3 and continue with: 38 / 64

On to step 4:
64 can be fit into 38 0 times, resulting in a remainder of 38.
The next digit of our result is 0. 
Result so far: 100.0
The remainder is 38 after subtracting 0 from 38.
Bring next digit (7) of the dividend behind the 38 and repeat the process: 387 / 64

Advancing to step 5:
If we divide 387 by 64, we get 6 and a remainder of 3.
Write down 6 as next digit of the result. 
Result so far: 1006.0
Subtract 384 from 387 to get 3.
Bring next digit (2) of the dividend behind the 3 and repeat the process: 32 / 64

Advancing to step 6:
When dividing 32 by 64, we get 0 with a remainder of 32.
Use 0 as the next digit of our solution. 
Result so far: 10060.0
Subtract 0 from 32 to get 32.
Since there are no more digits in the dividend, we add a zero to the remainder making it 320, and continue the process.

Going ahead to step 7:
64 goes into 320 5 times with a remainder of 0.
Use 5 as the next digit of our solution. 
Result so far: 10060.5
Subtract 320 from 320 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.

On to step 8:
64 goes into 0 0 times with a remainder of 0.
The next digit of our result is 0. 
Result so far: 10060.5
Subtract 0 from 0 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.

Going ahead to step 9:
0 divided by 64 is 0 with a remainder of 0.
Put 0 as the next digit of the answer. 
Result so far: 10060.5
The remainder is 0 after subtracting 0 from 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

After the division, we end up with 10060.5 and a remainder of 0.0.