OK, let's do this. We've got 7804 and 623 and we're adding them all together.

Step 1: We'll start by adding the digits 4 & 3 in column 1 and get 7.

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

Step 3: We'll start by adding the digits 8 & 6 in column 3 and get 14.
We'll write down the last digit 4 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 7 & 0 in column 4 and get 8.

So, 7804 + 623 = 8427.

