Let's break this down. We're going to add 3090 and 4790 together.

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

Step 2: We'll start by adding the digits 9 & 9 in column 2 and get 18.
We'll write down the last digit 8 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 0 & 7 in column 3 and get 8.

Step 4: We'll start by adding the digits 3 & 4 in column 4 and get 7.

So, 3090 + 4790 = 7880.

