Okay, we are given 6204 and 1355. Let's add them up step by step.

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

Step 2: We'll start by adding the digits 0 & 5 in column 2 and get 5.

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 6 & 1 in column 4 and get 7.

So, 6204 + 1355 = 7559.

