We've got two numbers: 3931 and 6005. Let's find their sum.

Step 1: We'll start by adding the digits 1 & 5 in column 1 and get 6.

Step 2: We'll start by adding the digits 3 & 0 in column 2 and get 3.

Step 3: We'll start by adding the digits 9 & 0 in column 3 and get 9.

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

So, 3931 + 6005 = 9936.

