Okay, we are given 5215 and 3663. Let's add them up step by step.

Step 1: We'll start by adding the digits 5 & 3 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 2 & 6 in column 3 and get 8.

Step 4: We'll start by adding the digits 5 & 3 in column 4 and get 8.

So, 5215 + 3663 = 8878.

