No problem, let's work through this together. We're starting with 3355 and 3303 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 5 & 0 in column 2 and get 5.

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

Step 4: We'll start by adding the digits 3 & 3 in column 4 and get 6.

So, 3355 + 3303 = 6658.

