Let's solve this addition problem. We have 400 and 84, and we need to add 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 0 & 8 in column 2 and get 8.

Step 3: We'll start by adding the digits 4 & 0 in column 3 and get 4.

So, 400 + 84 = 484.

