OK, let's do this. We've got 3131 and 1247 and we're adding them all together.

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

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

So, 3131 + 1247 = 4378.

