Let's break this down. We're going to add 3378 and 5611 together.

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

Step 2: We'll start by adding the digits 7 & 1 in column 2 and get 8.

Step 3: We'll start by adding the digits 3 & 6 in column 3 and get 9.

Step 4: We'll start by adding the digits 3 & 5 in column 4 and get 8.

So, 3378 + 5611 = 8989.

