Okay, we are tasked with adding 721 and 3042. Let's begin!

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

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 7 & 0 in column 3 and get 7.

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

So, 721 + 3042 = 3763.

