OK, let's do this. We've got 4512 and 2331 and we're adding them all together.

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

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

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

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

So, 4512 + 2331 = 6843.

