Okay, we are given 4391 and 3600. Let's add them up step by step.

Step 1: We'll start by adding the digits 1 & 0 in column 1 and get 1.

Step 2: We'll start by adding the digits 9 & 0 in column 2 and get 9.

Step 3: We'll start by adding the digits 3 & 6 in column 3 and get 9.

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

So, 4391 + 3600 = 7991.

