Okay, we are given 3015 and 3400. Let's add them up step by step.

Step 1: We'll start by adding the digits 5 & 0 in column 1 and get 5.

Step 2: We'll start by adding the digits 1 & 0 in column 2 and get 1.

Step 3: We'll start by adding the digits 0 & 4 in column 3 and get 4.

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

So, 3015 + 3400 = 6415.

