Alright, let's solve this problem step by step. We have 125 and 540 and we're adding them together.

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 2 & 4 in column 2 and get 6.

Step 3: We'll start by adding the digits 1 & 5 in column 3 and get 6.

So, 125 + 540 = 665.

