We are presented with 2603 and 5212. Let's work out the sum.

Step 1: We'll start by adding the digits 3 & 2 in column 1 and get 5.

Step 2: We'll start by adding the digits 0 & 1 in column 2 and get 1.

Step 3: We'll start by adding the digits 6 & 2 in column 3 and get 8.

Step 4: We'll start by adding the digits 2 & 5 in column 4 and get 7.

So, 2603 + 5212 = 7815.

