20400 ÷ 6 = 3400 R0
Let's divide 20400 by 6.

Step 1:
6 goes into 2 0 times with a remainder of 2.
Write down 0 as next digit of of the result. 
Result so far: 0
Subtract 0 from 2 to get 2.
Bring next digit (0) of the dividend behind the 2 and repeat the process: 20 / 6

Step 2:
6 goes into 20 3 times with a remainder of 2.
Write down 3 as next digit of of the result. 
Result so far: 3
Subtract 18 from 20 to get 2.
Bring next digit (4) of the dividend behind the 2 and repeat the process: 24 / 6

Step 3:
6 goes into 24 4 times with a remainder of 0.
Write down 4 as next digit of of the result. 
Result so far: 34
Subtract 24 from 24 to get 0.
Bring next digit (0) of the dividend behind the 0 and repeat the process: 0 / 6

Step 4:
6 goes into 0 0 times with a remainder of 0.
Write down 0 as next digit of of the result. 
Result so far: 340
Subtract 0 from 0 to get 0.
Bring next digit (0) of the dividend behind the 0 and repeat the process: 0 / 6

Step 5:
6 goes into 0 0 times with a remainder of 0.
Write down 0 as next digit of of the result. 
Result so far: 3400
Subtract 0 from 0 to get 0.

The final result is 3400 with a remainder of 0.