We're dividing 18511421 by 3 
We're looking to find how many times 3 goes into 18511421.

On to step 1:
3 goes into 1 0 times with a remainder of 1.
Write down 0 as next digit of the result. 
Result so far: 0.0
Deduct 0 from 1 and we're left with 1.
Include the next digit (8) from the dividend after 1, then repeat: 18 / 3

Going ahead to step 2:
If we divide 18 by 3, we get 6 and a remainder of 0.
The number 6 becomes the next digit in our result. 
Result so far: 6.0
Deduct 18 from 18 and we're left with 0.
Take the next digit (5) from the dividend and append it to 0, then repeat: 5 / 3

On to step 3:
If we divide 5 by 3, we get 1 and a remainder of 2.
Record the quotient 1 as the next digit in the result. 
Result so far: 61.0
Subtract 3 from 5 to get 2.
Fetch the next digit (1) from the dividend, attach it to 2 and continue: 21 / 3

Step 4:
If we divide 21 by 3, we get 7 and a remainder of 0.
Record the quotient 7 as the next digit in the result. 
Result so far: 617.0
The remainder is 0 after subtracting 21 from 21.
Bring next digit (1) of the dividend behind the 0 and repeat the process: 1 / 3

On to step 5:
3 can be fit into 1 0 times, resulting in a remainder of 1.
Put 0 as the next digit of the answer. 
Result so far: 6170.0
Subtract 0 from 1 to get 1.
Grab the next digit (4) from the dividend, add it to 1, then carry on: 14 / 3

Moving on to step 6:
The number 3 fits into 14 4 times, leaving a remainder of 2.
Use 4 as the next digit of our solution. 
Result so far: 61704.0
If we take 12 away from 14, we end up with 2.
Fetch the next digit (2) from the dividend, attach it to 2 and continue: 22 / 3

Moving on to step 7:
If we divide 22 by 3, we get 7 and a remainder of 1.
Put 7 as the next digit of the answer. 
Result so far: 617047.0
Deduct 21 from 22 and we're left with 1.
Grab the next digit (1) from the dividend, add it to 1, then carry on: 11 / 3

Step 8:
11 divided by 3 is 3 with a remainder of 2.
The next digit of our result is 3. 
Result so far: 6170473.0
If we take 9 away from 11, we end up with 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

Moving on to step 9:
3 goes into 20 6 times with a remainder of 2.
The number 6 becomes the next digit in our result. 
Result so far: 6170473.6
Subtracting 18 from 20 leaves us with 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

Going ahead to step 10:
The number 3 fits into 20 6 times, leaving a remainder of 2.
The number 6 becomes the next digit in our result. 
Result so far: 6170473.66
If we take 18 away from 20, we end up with 2.
Since there are no more digits in the dividend, we add a zero to the remainder making it 20, and continue the process.

The final outcome is 6170473.66, with a leftover of 0.002.