Alright, let's solve this problem step by step. We have 6604 and 40 and we're adding them together.

Step 1: We'll start by adding the digits 4 & 0 in column 1 and get 4.

Step 2: We'll start by adding the digits 0 & 4 in column 2 and get 4.

Step 3: We'll start by adding the digits 6 & 0 in column 3 and get 6.

Step 4: We'll start by adding the digits 6 & 0 in column 4 and get 6.

So, 6604 + 40 = 6644.

