Alright, let's solve this problem step by step. We have 120 and 3 and we're adding them together.

Step 1: We'll start by adding the digits 0 & 3 in column 1 and get 3.

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

Step 3: We'll start by adding the digits 1 & 0 in column 3 and get 1.

So, 120 + 3 = 123.

