Alright, let's solve this problem step by step. We have 4521 and 66 and we're adding them together.

Step 1: We'll start by adding the digits 1 & 6 in column 1 and get 7.

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

Step 3: We'll start by adding the digits 5 & 0 in column 3 and get 5.

Step 4: We'll start by adding the digits 4 & 0 in column 4 and get 4.

So, 4521 + 66 = 4587.

