54123 ÷ 3 = 18041 R0
Let's divide 54123 by 3.

Step 1:
3 goes into 5 1 times with a remainder of 2.
Write down 1 as next digit of of the result. 
Result so far: 1
Subtract 3 from 5 to get 2.
Bring next digit (4) of the dividend behind the 2 and repeat the process: 24 / 3

Step 2:
3 goes into 24 8 times with a remainder of 0.
Write down 8 as next digit of of the result. 
Result so far: 18
Subtract 24 from 24 to get 0.
Bring next digit (1) of the dividend behind the 0 and repeat the process: 1 / 3

Step 3:
3 goes into 1 0 times with a remainder of 1.
Write down 0 as next digit of of the result. 
Result so far: 180
Subtract 0 from 1 to get 1.
Bring next digit (2) of the dividend behind the 1 and repeat the process: 12 / 3

Step 4:
3 goes into 12 4 times with a remainder of 0.
Write down 4 as next digit of of the result. 
Result so far: 1804
Subtract 12 from 12 to get 0.
Bring next digit (3) of the dividend behind the 0 and repeat the process: 3 / 3

Step 5:
3 goes into 3 1 times with a remainder of 0.
Write down 1 as next digit of of the result. 
Result so far: 18041
Subtract 3 from 3 to get 0.

The final result is 18041 with a remainder of 0.