We look at the division of 42721159 by 399 
The aim is to understand the frequency of 399 in 42721159.

Advancing to step 1:
4 divided by 399 is 0 with a remainder of 4.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
Subtracting 0 from 4 leaves us with 4.
Bring next digit (2) of the dividend behind the 4 and repeat the process: 42 / 399

On to step 2:
42 divided by 399 is 0 with a remainder of 42.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
If we take 0 away from 42, we end up with 42.
Bring next digit (7) of the dividend behind the 42 and repeat the process: 427 / 399

Moving on to step 3:
399 can be fit into 427 1 times, resulting in a remainder of 28.
Record the quotient 1 as the next digit in the result. 
Result so far: 1.0
If we subtract 399 from 427, we get 28.
Append the next digit (2) from the dividend to 28 and continue with: 282 / 399

Going ahead to step 4:
399 goes into 282 0 times with a remainder of 282.
Use 0 as the next digit of our solution. 
Result so far: 10.0
If we subtract 0 from 282, we get 282.
Bring next digit (1) of the dividend behind the 282 and repeat the process: 2821 / 399

Let's proceed to step 5:
2821 divided by 399 is 7 with a remainder of 28.
Record the quotient 7 as the next digit in the result. 
Result so far: 107.0
Deduct 2793 from 2821 and we're left with 28.
Append the next digit (1) from the dividend to 28 and continue with: 281 / 399

Moving on to step 6:
If we divide 281 by 399, we get 0 and a remainder of 281.
The next digit of our result is 0. 
Result so far: 1070.0
The remainder is 281 after subtracting 0 from 281.
Grab the next digit (5) from the dividend, add it to 281, then carry on: 2815 / 399

Moving on to step 7:
If we divide 2815 by 399, we get 7 and a remainder of 22.
Use 7 as the next digit of our solution. 
Result so far: 10707.0
If we subtract 2793 from 2815, we get 22.
Grab the next digit (9) from the dividend, add it to 22, then carry on: 229 / 399

Advancing to step 8:
229 divided by 399 is 0 with a remainder of 229.
Record the quotient 0 as the next digit in the result. 
Result so far: 107070.0
Deduct 0 from 229 and we're left with 229.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2290, and continue the process.

Advancing to step 9:
399 goes into 2290 5 times with a remainder of 295.
Record the quotient 5 as the next digit in the result. 
Result so far: 107070.5
Subtract 1995 from 2290 to get 295.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2950, and continue the process.

Let's proceed to step 10:
399 goes into 2950 7 times with a remainder of 157.
Write down 7 as next digit of the result. 
Result so far: 107070.57
The remainder is 157 after subtracting 2793 from 2950.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1570, and continue the process.

On to step 11:
399 goes into 1570 3 times with a remainder of 373.
Record the quotient 3 as the next digit in the result. 
Result so far: 107070.573
Subtracting 1197 from 1570 leaves us with 373.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3730, and continue the process.

Advancing to step 12:
The number 399 fits into 3730 9 times, leaving a remainder of 139.
Use 9 as the next digit of our solution. 
Result so far: 107070.5739
Deduct 3591 from 3730 and we're left with 139.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1390, and continue the process.

On to step 13:
The number 399 fits into 1390 3 times, leaving a remainder of 193.
Use 3 as the next digit of our solution. 
Result so far: 107070.57393
Deduct 1197 from 1390 and we're left with 193.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1930, and continue the process.

Moving on to step 14:
The number 399 fits into 1930 4 times, leaving a remainder of 334.
Use 4 as the next digit of our solution. 
Result so far: 107070.573934
Subtracting 1596 from 1930 leaves us with 334.
Since there are no more digits in the dividend, we add a zero to the remainder making it 3340, and continue the process.

Moving on to step 15:
399 can be fit into 3340 8 times, resulting in a remainder of 148.
Write down 8 as next digit of the result. 
Result so far: 107070.5739348
If we take 3192 away from 3340, we end up with 148.
Since there are no more digits in the dividend, we add a zero to the remainder making it 1480, and continue the process.

Advancing to step 16:
1480 divided by 399 is 3 with a remainder of 283.
The next digit of our result is 3. 
Result so far: 107070.57393483
Subtract 1197 from 1480 to get 283.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2830, and continue the process.

The final outcome is 107070.57393483, with a leftover of 2.83e-07.