No problem, let's work through this together. We're starting with 8784 and 7861 and adding them all up.

Step 1: We'll start by adding the digits 4 & 1 in column 1 and get 5.

Step 2: We'll start by adding the digits 8 & 6 in column 2 and get 14.
We'll write down the last digit 4 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 7 & 8 in column 3 and get 16.
We'll write down the last digit 6 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 8 & 7 in column 4 and get 16.
We'll write down the last digit 6 and carry the 1 to the next column.

So, 8784 + 7861 = 16645.

