Let's divide 79515423 by 645
The aim is to understand the frequency of 645 in 79515423.

Step 1:
If we divide 7 by 645, we get 0 and a remainder of 7.
Write down 0 as next digit of the result. 
Result so far: 0.0
If we take 0 away from 7, we end up with 7.
Bring next digit (9) of the dividend behind the 7 and repeat the process: 79 / 645

Advancing to step 2:
645 goes into 79 0 times with a remainder of 79.
Put 0 as the next digit of the answer. 
Result so far: 0.0
If we subtract 0 from 79, we get 79.
Bring next digit (5) of the dividend behind the 79 and repeat the process: 795 / 645

Let's proceed to step 3:
When dividing 795 by 645, we get 1 with a remainder of 150.
The next digit of our result is 1. 
Result so far: 1.0
The remainder is 150 after subtracting 645 from 795.
Include the next digit (1) from the dividend after 150, then repeat: 1501 / 645

Let's proceed to step 4:
When dividing 1501 by 645, we get 2 with a remainder of 211.
Use 2 as the next digit of our solution. 
Result so far: 12.0
Deduct 1290 from 1501 and we're left with 211.
Bring next digit (5) of the dividend behind the 211 and repeat the process: 2115 / 645

On to step 5:
The number 645 fits into 2115 3 times, leaving a remainder of 180.
The number 3 becomes the next digit in our result. 
Result so far: 123.0
Deduct 1935 from 2115 and we're left with 180.
Bring next digit (4) of the dividend behind the 180 and repeat the process: 1804 / 645

Going ahead to step 6:
1804 divided by 645 is 2 with a remainder of 514.
Use 2 as the next digit of our solution. 
Result so far: 1232.0
The remainder is 514 after subtracting 1290 from 1804.
Include the next digit (2) from the dividend after 514, then repeat: 5142 / 645

Advancing to step 7:
645 can be fit into 5142 7 times, resulting in a remainder of 627.
Write down 7 as next digit of the result. 
Result so far: 12327.0
Subtracting 4515 from 5142 leaves us with 627.
Append the next digit (3) from the dividend to 627 and continue with: 6273 / 645

Moving on to step 8:
If we divide 6273 by 645, we get 9 and a remainder of 468.
Record the quotient 9 as the next digit in the result. 
Result so far: 123279.0
If we take 5805 away from 6273, we end up with 468.
Since there are no more digits in the dividend, we add a zero to the remainder making it 4680, and continue the process.

Advancing to step 9:
645 goes into 4680 7 times with a remainder of 165.
The number 7 becomes the next digit in our result. 
Result so far: 123279.7
Subtract 4515 from 4680 to get 165.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1650, and continue the process.

On to step 10:
When dividing 1650 by 645, we get 2 with a remainder of 360.
Use 2 as the next digit of our solution. 
Result so far: 123279.72
If we subtract 1290 from 1650, we get 360.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3600, and continue the process.

Moving on to step 11:
If we divide 3600 by 645, we get 5 and a remainder of 375.
The next digit of our result is 5. 
Result so far: 123279.725
Subtract 3225 from 3600 to get 375.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3750, and continue the process.

Advancing to step 12:
When dividing 3750 by 645, we get 5 with a remainder of 525.
The next digit of our result is 5. 
Result so far: 123279.7255
Subtracting 3225 from 3750 leaves us with 525.
Since there are no more digits in the dividend, we add a zero to the remainder making it 5250, and continue the process.

The final result is 123279.7255 with a remainder of 0.00525.