12129 divided by 90 
Our goal is to divide 12129 by 90.

Step 1:
90 goes into 1 0 times with a remainder of 1.
Write down 0 as next digit of the result. 
Result so far: 0.0
Subtracting 0 from 1 leaves us with 1.
Fetch the next digit (2) from the dividend, attach it to 1 and continue: 12 / 90

Advancing to step 2:
When dividing 12 by 90, we get 0 with a remainder of 12.
Put 0 as the next digit of the answer. 
Result so far: 0.0
If we take 0 away from 12, we end up with 12.
Fetch the next digit (1) from the dividend, attach it to 12 and continue: 121 / 90

On to step 3:
121 divided by 90 is 1 with a remainder of 31.
Write down 1 as next digit of the result. 
Result so far: 1.0
Deduct 90 from 121 and we're left with 31.
Include the next digit (2) from the dividend after 31, then repeat: 312 / 90

Going ahead to step 4:
312 divided by 90 is 3 with a remainder of 42.
Record the quotient 3 as the next digit in the result. 
Result so far: 13.0
If we subtract 270 from 312, we get 42.
Include the next digit (9) from the dividend after 42, then repeat: 429 / 90

Step 5:
90 can be fit into 429 4 times, resulting in a remainder of 69.
Put 4 as the next digit of the answer. 
Result so far: 134.0
The remainder is 69 after subtracting 360 from 429.
Since there are no more digits in the dividend, we add a zero to the remainder making it 690, and continue the process.

Step 6:
90 can be fit into 690 7 times, resulting in a remainder of 60.
Record the quotient 7 as the next digit in the result. 
Result so far: 134.7
If we subtract 630 from 690, we get 60.
Since there are no more digits in the dividend, we add a zero to the remainder making it 600, and continue the process.

Step 7:
If we divide 600 by 90, we get 6 and a remainder of 60.
Write down 6 as next digit of the result. 
Result so far: 134.76
If we subtract 540 from 600, we get 60.
Since there are no more digits in the dividend, we add a zero to the remainder making it 600, and continue the process.

Let's proceed to step 8:
When dividing 600 by 90, we get 6 with a remainder of 60.
Write down 6 as next digit of the result. 
Result so far: 134.766
The remainder is 60 after subtracting 540 from 600.
Since there are no more digits in the dividend, we add a zero to the remainder making it 600, and continue the process.

The final result is 134.766 with a remainder of 0.006.