Let's break this down. We're going to add 1040 and 4359 together.

Step 1: We'll start by adding the digits 0 & 9 in column 1 and get 9.

Step 2: We'll start by adding the digits 4 & 5 in column 2 and get 9.

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

Step 4: We'll start by adding the digits 1 & 4 in column 4 and get 5.

So, 1040 + 4359 = 5399.

