Not to worry, we've got 4013 and 3986. Let's get to adding them!

Step 1: We'll start by adding the digits 3 & 6 in column 1 and get 9.

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

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

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

So, 4013 + 3986 = 7999.

