Okay, we are tasked with adding 6981 and 18. Let's begin!

Step 1: We'll start by adding the digits 1 & 8 in column 1 and get 9.

Step 2: We'll start by adding the digits 8 & 1 in column 2 and get 9.

Step 3: We'll start by adding the digits 9 & 0 in column 3 and get 9.

Step 4: We'll start by adding the digits 6 & 0 in column 4 and get 6.

So, 6981 + 18 = 6999.

