Let's break this down. We're going to add 643676285 and 582707880 together.

Step 1: We'll start by adding the digits 5 & 0 in column 1 and get 5.

Step 2: We'll start by adding the digits 8 & 8 in column 2 and get 16.
We'll write down the last digit 6 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 2 & 8 in column 3 and get 11.
We'll write down the last digit 1 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 6 & 7 in column 4 and get 14.
We'll write down the last digit 4 and carry the 1 to the next column.

Step 5: We'll start by adding the digits 7 & 0 in column 5 and get 8.

Step 6: We'll start by adding the digits 6 & 7 in column 6 and get 13.
We'll write down the last digit 3 and carry the 1 to the next column.

Step 7: We'll start by adding the digits 3 & 2 in column 7 and get 6.

Step 8: We'll start by adding the digits 4 & 8 in column 8 and get 12.
We'll write down the last digit 2 and carry the 1 to the next column.

Step 9: We'll start by adding the digits 6 & 5 in column 9 and get 12.
We'll write down the last digit 2 and carry the 1 to the next column.

So, 643676285 + 582707880 = 1226384165.

