Let's break this down. We're going to add 1271 and 8400 together.

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

Step 2: We'll start by adding the digits 7 & 0 in column 2 and get 7.

Step 3: We'll start by adding the digits 2 & 4 in column 3 and get 6.

Step 4: We'll start by adding the digits 1 & 8 in column 4 and get 9.

So, 1271 + 8400 = 9671.

