Alright, let's solve this problem step by step. We have 5221 and 2578 and we're adding them together.

Step 1: We'll start by adding the digits 1 & 8 in column 1 and get 9.

Step 2: We'll start by adding the digits 2 & 7 in column 2 and get 9.

Step 3: We'll start by adding the digits 2 & 5 in column 3 and get 7.

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

So, 5221 + 2578 = 7799.

