No problem, let's work through this together. We're starting with 355490973 and 400768515 and adding them all up.

Step 1: We'll start by adding the digits 3 & 5 in column 1 and get 8.

Step 2: We'll start by adding the digits 7 & 1 in column 2 and get 8.

Step 3: We'll start by adding the digits 9 & 5 in column 3 and get 14.
We'll write down the last digit 4 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 0 & 8 in column 4 and get 9.

Step 5: We'll start by adding the digits 9 & 6 in column 5 and get 15.
We'll write down the last digit 5 and carry the 1 to the next column.

Step 6: We'll start by adding the digits 4 & 7 in column 6 and get 12.
We'll write down the last digit 2 and carry the 1 to the next column.

Step 7: We'll start by adding the digits 5 & 0 in column 7 and get 6.

Step 8: We'll start by adding the digits 5 & 0 in column 8 and get 5.

Step 9: We'll start by adding the digits 3 & 4 in column 9 and get 7.

So, 355490973 + 400768515 = 756259488.

