We're dividing 43091593 by 645 
The aim is to understand the frequency of 645 in 43091593.

Step 1:
645 can be fit into 4 0 times, resulting in a remainder of 4.
Write down 0 as next digit of the result. 
Result so far: 0.0
The remainder is 4 after subtracting 0 from 4.
Bring next digit (3) of the dividend behind the 4 and repeat the process: 43 / 645

Step 2:
645 goes into 43 0 times with a remainder of 43.
Use 0 as the next digit of our solution. 
Result so far: 0.0
The remainder is 43 after subtracting 0 from 43.
Bring next digit (0) of the dividend behind the 43 and repeat the process: 430 / 645

Step 3:
645 goes into 430 0 times with a remainder of 430.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Deduct 0 from 430 and we're left with 430.
Append the next digit (9) from the dividend to 430 and continue with: 4309 / 645

Step 4:
645 goes into 4309 6 times with a remainder of 439.
The next digit of our result is 6. 
Result so far: 6.0
The remainder is 439 after subtracting 3870 from 4309.
Include the next digit (1) from the dividend after 439, then repeat: 4391 / 645

Going ahead to step 5:
4391 divided by 645 is 6 with a remainder of 521.
The number 6 becomes the next digit in our result. 
Result so far: 66.0
If we take 3870 away from 4391, we end up with 521.
Fetch the next digit (5) from the dividend, attach it to 521 and continue: 5215 / 645

Advancing to step 6:
645 goes into 5215 8 times with a remainder of 55.
Use 8 as the next digit of our solution. 
Result so far: 668.0
If we take 5160 away from 5215, we end up with 55.
Append the next digit (9) from the dividend to 55 and continue with: 559 / 645

Let's proceed to step 7:
The number 645 fits into 559 0 times, leaving a remainder of 559.
The next digit of our result is 0. 
Result so far: 6680.0
Subtract 0 from 559 to get 559.
Fetch the next digit (3) from the dividend, attach it to 559 and continue: 5593 / 645

On to step 8:
645 can be fit into 5593 8 times, resulting in a remainder of 433.
The next digit of our result is 8. 
Result so far: 66808.0
The remainder is 433 after subtracting 5160 from 5593.
Since there are no more digits in the dividend, we add a zero to the remainder making it 4330, and continue the process.

Going ahead to step 9:
The number 645 fits into 4330 6 times, leaving a remainder of 460.
The next digit of our result is 6. 
Result so far: 66808.6
Deduct 3870 from 4330 and we're left with 460.
Since there are no more digits in the dividend, we add a zero to the remainder making it 4600, and continue the process.

Moving on to step 10:
645 goes into 4600 7 times with a remainder of 85.
Record the quotient 7 as the next digit in the result. 
Result so far: 66808.67
If we take 4515 away from 4600, we end up with 85.
Since there are no more digits in the dividend, we add a zero to the remainder making it 850, and continue the process.

Step 11:
850 divided by 645 is 1 with a remainder of 205.
Put 1 as the next digit of the answer. 
Result so far: 66808.671
If we take 645 away from 850, we end up with 205.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2050, and continue the process.

Moving on to step 12:
645 goes into 2050 3 times with a remainder of 115.
The next digit of our result is 3. 
Result so far: 66808.6713
The remainder is 115 after subtracting 1935 from 2050.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1150, and continue the process.

On to step 13:
When dividing 1150 by 645, we get 1 with a remainder of 505.
Use 1 as the next digit of our solution. 
Result so far: 66808.67131
Subtract 645 from 1150 to get 505.
Since there are no more digits in the dividend, we add a zero to the remainder making it 5050, and continue the process.

On to step 14:
When dividing 5050 by 645, we get 7 with a remainder of 535.
Put 7 as the next digit of the answer. 
Result so far: 66808.671317
Subtract 4515 from 5050 to get 535.
Since there are no more digits in the dividend, we add a zero to the remainder making it 5350, and continue the process.

Moving on to step 15:
645 goes into 5350 8 times with a remainder of 190.
Record the quotient 8 as the next digit in the result. 
Result so far: 66808.6713178
If we subtract 5160 from 5350, we get 190.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1900, and continue the process.

Let's proceed to step 16:
645 goes into 1900 2 times with a remainder of 610.
Use 2 as the next digit of our solution. 
Result so far: 66808.67131782
Subtract 1290 from 1900 to get 610.
Since there are no more digits in the dividend, we add a zero to the remainder making it 6100, and continue the process.

After the division, we end up with 66808.67131782 and a remainder of 6.1e-07.