We are presented with 8610 and 8409. Let's work out the sum.

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

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

Step 3: We'll start by adding the digits 6 & 4 in column 3 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 8 & 8 in column 4 and get 17.
We'll write down the last digit 7 and carry the 1 to the next column.

So, 8610 + 8409 = 17019.

