12072135 ÷ 521 
Our goal is to divide 12072135 by 521.

Step 1:
521 goes into 1 0 times with a remainder of 1.
Put 0 as the next digit of the answer. 
Result so far: 0.0
The remainder is 1 after subtracting 0 from 1.
Include the next digit (2) from the dividend after 1, then repeat: 12 / 521

Moving on to step 2:
If we divide 12 by 521, we get 0 and a remainder of 12.
Use 0 as the next digit of our solution. 
Result so far: 0.0
If we take 0 away from 12, we end up with 12.
Append the next digit (0) from the dividend to 12 and continue with: 120 / 521

Moving on to step 3:
120 divided by 521 is 0 with a remainder of 120.
Write down 0 as next digit of the result. 
Result so far: 0.0
If we take 0 away from 120, we end up with 120.
Include the next digit (7) from the dividend after 120, then repeat: 1207 / 521

On to step 4:
The number 521 fits into 1207 2 times, leaving a remainder of 165.
The number 2 becomes the next digit in our result. 
Result so far: 2.0
Subtracting 1042 from 1207 leaves us with 165.
Fetch the next digit (2) from the dividend, attach it to 165 and continue: 1652 / 521

Step 5:
521 goes into 1652 3 times with a remainder of 89.
Use 3 as the next digit of our solution. 
Result so far: 23.0
Deduct 1563 from 1652 and we're left with 89.
Fetch the next digit (1) from the dividend, attach it to 89 and continue: 891 / 521

Advancing to step 6:
If we divide 891 by 521, we get 1 and a remainder of 370.
Write down 1 as next digit of the result. 
Result so far: 231.0
Subtracting 521 from 891 leaves us with 370.
Take the next digit (3) from the dividend and append it to 370, then repeat: 3703 / 521

Step 7:
If we divide 3703 by 521, we get 7 and a remainder of 56.
The number 7 becomes the next digit in our result. 
Result so far: 2317.0
Subtracting 3647 from 3703 leaves us with 56.
Append the next digit (5) from the dividend to 56 and continue with: 565 / 521

Let's proceed to step 8:
565 divided by 521 is 1 with a remainder of 44.
Record the quotient 1 as the next digit in the result. 
Result so far: 23171.0
Deduct 521 from 565 and we're left with 44.
Since there are no more digits in the dividend, we add a zero to the remainder making it 440, and continue the process.

Going ahead to step 9:
The number 521 fits into 440 0 times, leaving a remainder of 440.
The number 0 becomes the next digit in our result. 
Result so far: 23171.0
Subtract 0 from 440 to get 440.
Since there are no more digits in the dividend, we add a zero to the remainder making it 4400, and continue the process.

Let's proceed to step 10:
When dividing 4400 by 521, we get 8 with a remainder of 232.
Use 8 as the next digit of our solution. 
Result so far: 23171.08
The remainder is 232 after subtracting 4168 from 4400.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2320, and continue the process.

Moving on to step 11:
If we divide 2320 by 521, we get 4 and a remainder of 236.
The number 4 becomes the next digit in our result. 
Result so far: 23171.084
Subtracting 2084 from 2320 leaves us with 236.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2360, and continue the process.

Moving on to step 12:
The number 521 fits into 2360 4 times, leaving a remainder of 276.
The next digit of our result is 4. 
Result so far: 23171.0844
Subtracting 2084 from 2360 leaves us with 276.
Since there are no more digits in the dividend, we add a zero to the remainder making it 2760, and continue the process.

The final outcome is 23171.0844, with a leftover of 0.00276.