Okay, we are tasked with adding 399 and 5130. Let's begin!

Step 1: We'll start by adding the digits 9 & 0 in column 1 and get 9.

Step 2: We'll start by adding the digits 9 & 3 in column 2 and get 12.
We'll write down the last digit 2 and carry the 1 to the next column.

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

Step 4: We'll start by adding the digits 0 & 5 in column 4 and get 5.

So, 399 + 5130 = 5529.

