We are presented with 264612635 and 7126877893. Let's work out the sum.

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

Step 2: We'll start by adding the digits 3 & 9 in column 2 and get 12.
We'll write down the last digit 2 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 6 & 8 in column 3 and get 15.
We'll write down the last digit 5 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 2 & 7 in column 4 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

Step 5: We'll start by adding the digits 1 & 7 in column 5 and get 9.

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

Step 7: We'll start by adding the digits 4 & 6 in column 7 and get 11.
We'll write down the last digit 1 and carry the 1 to the next column.

Step 8: We'll start by adding the digits 6 & 2 in column 8 and get 9.

Step 9: We'll start by adding the digits 2 & 1 in column 9 and get 3.

Step 10: We'll start by adding the digits 0 & 7 in column 10 and get 7.

So, 264612635 + 7126877893 = 7391490528.

