Let's solve this addition problem. We have 1003 and 504, and we need to add them together.

Step 1: We'll start by adding the digits 3 & 4 in column 1 and get 7.

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 0 & 5 in column 3 and get 5.

Step 4: We'll start by adding the digits 1 & 0 in column 4 and get 1.

So, 1003 + 504 = 1507.

