851409 ÷ 80 
Our goal is to divide 851409 by 80.

On to step 1:
The number 80 fits into 8 0 times, leaving a remainder of 8.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Subtract 0 from 8 to get 8.
Bring next digit (5) of the dividend behind the 8 and repeat the process: 85 / 80

Let's proceed to step 2:
When dividing 85 by 80, we get 1 with a remainder of 5.
The number 1 becomes the next digit in our result. 
Result so far: 1.0
Deduct 80 from 85 and we're left with 5.
Bring next digit (1) of the dividend behind the 5 and repeat the process: 51 / 80

Advancing to step 3:
If we divide 51 by 80, we get 0 and a remainder of 51.
The next digit of our result is 0. 
Result so far: 10.0
Subtract 0 from 51 to get 51.
Include the next digit (4) from the dividend after 51, then repeat: 514 / 80

Going ahead to step 4:
When dividing 514 by 80, we get 6 with a remainder of 34.
Use 6 as the next digit of our solution. 
Result so far: 106.0
Deduct 480 from 514 and we're left with 34.
Take the next digit (0) from the dividend and append it to 34, then repeat: 340 / 80

On to step 5:
When dividing 340 by 80, we get 4 with a remainder of 20.
Record the quotient 4 as the next digit in the result. 
Result so far: 1064.0
Deduct 320 from 340 and we're left with 20.
Grab the next digit (9) from the dividend, add it to 20, then carry on: 209 / 80

Advancing to step 6:
80 goes into 209 2 times with a remainder of 49.
Record the quotient 2 as the next digit in the result. 
Result so far: 10642.0
Deduct 160 from 209 and we're left with 49.
Since there are no more digits in the dividend, we add a zero to the remainder making it 490, and continue the process.

Moving on to step 7:
The number 80 fits into 490 6 times, leaving a remainder of 10.
Write down 6 as next digit of the result. 
Result so far: 10642.6
If we subtract 480 from 490, we get 10.
Since there are no more digits in the dividend, we add a zero to the remainder making it 100, and continue the process.

On to step 8:
100 divided by 80 is 1 with a remainder of 20.
The next digit of our result is 1. 
Result so far: 10642.61
Subtracting 80 from 100 leaves us with 20.
Since there are no more digits in the dividend, we add a zero to the remainder making it 200, and continue the process.

Step 9:
80 can be fit into 200 2 times, resulting in a remainder of 40.
The number 2 becomes the next digit in our result. 
Result so far: 10642.612
Deduct 160 from 200 and we're left with 40.
Since there are no more digits in the dividend, we add a zero to the remainder making it 400, and continue the process.

Advancing to step 10:
If we divide 400 by 80, we get 5 and a remainder of 0.
Put 5 as the next digit of the answer. 
Result so far: 10642.6125
Subtract 400 from 400 to get 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

Advancing to step 11:
80 goes into 0 0 times with a remainder of 0.
Put 0 as the next digit of the answer. 
Result so far: 10642.6125
Subtract 0 from 0 to get 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

Moving on to step 12:
The number 80 fits into 0 0 times, leaving a remainder of 0.
Write down 0 as next digit of the result. 
Result so far: 10642.6125
If we take 0 away from 0, we end up with 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

The final result is 10642.6125 with a remainder of 0.0.