We have numbers 1203 and 3303. Let's start adding them together.

Step 1: We'll start by adding the digits 3 & 3 in column 1 and get 6.

Step 2: We'll start by adding the digits 0 & 0 in column 2 and get 0.

Step 3: We'll start by adding the digits 2 & 3 in column 3 and get 5.

Step 4: We'll start by adding the digits 1 & 3 in column 4 and get 4.

So, 1203 + 3303 = 4506.

