Let's get this math done. We have 8407 and 2015 and we're going to add them all together.

Step 1: We'll start by adding the digits 7 & 5 in column 1 and get 12.
We'll write down the last digit 2 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 0 & 1 in column 2 and get 2.

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

Step 4: We'll start by adding the digits 8 & 2 in column 4 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

So, 8407 + 2015 = 10422.

