Alright, let's solve this problem step by step. We have 39 and 615 and we're adding them together.

Step 1: We'll start by adding the digits 9 & 5 in column 1 and get 14.
We'll write down the last digit 4 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 3 & 1 in column 2 and get 5.

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

So, 39 + 615 = 654.

