We have numbers 9487 and 7391. Let's start adding them together.

Step 1: We'll start by adding the digits 7 & 1 in column 1 and get 8.

Step 2: We'll start by adding the digits 8 & 9 in column 2 and get 17.
We'll write down the last digit 7 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 4 & 3 in column 3 and get 8.

Step 4: We'll start by adding the digits 9 & 7 in column 4 and get 16.
We'll write down the last digit 6 and carry the 1 to the next column.

So, 9487 + 7391 = 16878.

