We are presented with 8623 and 1215. Let's work out the sum.

Step 1: We'll start by adding the digits 3 & 5 in column 1 and get 8.

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

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 8 & 1 in column 4 and get 9.

So, 8623 + 1215 = 9838.

