OK, let's do this. We've got 3004 and 2639 and we're adding them all together.

Step 1: We'll start by adding the digits 4 & 9 in column 1 and get 13.
We'll write down the last digit 3 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 0 & 3 in column 2 and get 4.

Step 3: We'll start by adding the digits 0 & 6 in column 3 and get 6.

Step 4: We'll start by adding the digits 3 & 2 in column 4 and get 5.

So, 3004 + 2639 = 5643.

