Okay, we are given 9398 and 8642. Let's add them up step by step.

Step 1: We'll start by adding the digits 8 & 2 in column 1 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 9 & 4 in column 2 and get 14.
We'll write down the last digit 4 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 3 & 6 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 9 & 8 in column 4 and get 18.
We'll write down the last digit 8 and carry the 1 to the next column.

So, 9398 + 8642 = 18040.

