Okay, we are tasked with adding 3090 and 1218. Let's begin!

Step 1: We'll start by adding the digits 0 & 8 in column 1 and get 8.

Step 2: We'll start by adding the digits 9 & 1 in column 2 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 0 & 2 in column 3 and get 3.

Step 4: We'll start by adding the digits 3 & 1 in column 4 and get 4.

So, 3090 + 1218 = 4308.

