We are presented with 4039 and 2309. Let's work out the sum.

Step 1: We'll start by adding the digits 9 & 9 in column 1 and get 18.
We'll write down the last digit 8 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 3 & 0 in column 2 and get 4.

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

Step 4: We'll start by adding the digits 4 & 2 in column 4 and get 6.

So, 4039 + 2309 = 6348.

