No problem, let's work through this together. We're starting with 3135 and 4204 and adding them all up.

Step 1: We'll start by adding the digits 5 & 4 in column 1 and get 9.

Step 2: We'll start by adding the digits 3 & 0 in column 2 and get 3.

Step 3: We'll start by adding the digits 1 & 2 in column 3 and get 3.

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

So, 3135 + 4204 = 7339.

