No problem, let's work through this together. We're starting with 778 and 125 and adding them all up.

Step 1: We'll start by adding the digits 8 & 5 in column 1 and get 13.
We'll write down the last digit 3 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 7 & 2 in column 2 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 7 & 1 in column 3 and get 9.

So, 778 + 125 = 903.

