OK, let's do this. We've got 2531 and 6039 and we're adding them all together.

Step 1: We'll start by adding the digits 1 & 9 in column 1 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 3 & 3 in column 2 and get 7.

Step 3: We'll start by adding the digits 5 & 0 in column 3 and get 5.

Step 4: We'll start by adding the digits 2 & 6 in column 4 and get 8.

So, 2531 + 6039 = 8570.

