Okay, we are given 5631 and 8404. Let's add them up step by step.

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

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

Step 3: We'll start by adding the digits 6 & 4 in column 3 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 5 & 8 in column 4 and get 14.
We'll write down the last digit 4 and carry the 1 to the next column.

So, 5631 + 8404 = 14035.

