Let's break this down. We're going to add 7904 and 7002 together.

Step 1: We'll start by adding the digits 4 & 2 in column 1 and get 6.

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

Step 3: We'll start by adding the digits 9 & 0 in column 3 and get 9.

Step 4: We'll start by adding the digits 7 & 7 in column 4 and get 14.
We'll write down the last digit 4 and carry the 1 to the next column.

So, 7904 + 7002 = 14906.

