Alright, let's solve this problem step by step. We have 558 and 431 and we're adding them together.

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

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

Step 3: We'll start by adding the digits 5 & 4 in column 3 and get 9.

So, 558 + 431 = 989.

