Let's break this down. We're going to add 7391 and 5186 together.

Step 1: We'll start by adding the digits 1 & 6 in column 1 and get 7.

Step 2: We'll start by adding the digits 9 & 8 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 3 & 1 in column 3 and get 5.

Step 4: We'll start by adding the digits 7 & 5 in column 4 and get 12.
We'll write down the last digit 2 and carry the 1 to the next column.

So, 7391 + 5186 = 12577.

