No problem, let's work through this together. We're starting with 7505 and 403 and adding them all up.

Step 1: We'll start by adding the digits 5 & 3 in column 1 and get 8.

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 5 & 4 in column 3 and get 9.

Step 4: We'll start by adding the digits 7 & 0 in column 4 and get 7.

So, 7505 + 403 = 7908.

