8403 ÷ 4 = 2100 R3
Alright, let's work through the division of 8403 by 4 step by step.

Step 1:
4 goes into 8 2 times with a remainder of 0.
Write down 2 as next digit of of the result. 
Result so far: 2
Subtract 8 from 8 to get 0.
Bring next digit (4) of the dividend behind the 0 and repeat the process: 4 / 4

Step 2:
4 goes into 4 1 times with a remainder of 0.
Write down 1 as next digit of of the result. 
Result so far: 21
Subtract 4 from 4 to get 0.
Bring next digit (0) of the dividend behind the 0 and repeat the process: 0 / 4

Step 3:
4 goes into 0 0 times with a remainder of 0.
Write down 0 as next digit of of the result. 
Result so far: 210
Subtract 0 from 0 to get 0.
Bring next digit (3) of the dividend behind the 0 and repeat the process: 3 / 4

Step 4:
4 goes into 3 0 times with a remainder of 3.
Write down 0 as next digit of of the result. 
Result so far: 2100
Subtract 0 from 3 to get 3.

The final result is 2100 with a remainder of 3.