Alright, let's solve this problem step by step. We have 90 and 504 and we're adding them together.

Step 1: We'll start by adding the digits 0 & 4 in column 1 and get 4.

Step 2: We'll start by adding the digits 9 & 0 in column 2 and get 9.

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

So, 90 + 504 = 594.

