OK, let's do this. We've got 2117 and 1261 and we're adding them all together.

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

Step 2: We'll start by adding the digits 1 & 6 in column 2 and get 7.

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

Step 4: We'll start by adding the digits 2 & 1 in column 4 and get 3.

So, 2117 + 1261 = 3378.

