We have numbers 3605 and 6393. Let's start adding them together.

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

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

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

Step 4: We'll start by adding the digits 3 & 6 in column 4 and get 9.

So, 3605 + 6393 = 9998.

