Let's get this math done. We have 1239 and 3012 and we're going to add them all together.

Step 1: We'll start by adding the digits 9 & 2 in column 1 and get 11.
We'll write down the last digit 1 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 3 & 1 in column 2 and get 5.

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

Step 4: We'll start by adding the digits 1 & 3 in column 4 and get 4.

So, 1239 + 3012 = 4251.

