Alright, let's solve this problem step by step. We have 4239660818 and 119900015 and we're adding them together.

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 1 & 1 in column 2 and get 3.

Step 3: We'll start by adding the digits 8 & 0 in column 3 and get 8.

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

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

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

Step 7: We'll start by adding the digits 9 & 9 in column 7 and get 19.
We'll write down the last digit 9 and carry the 1 to the next column.

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

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 4 & 0 in column 10 and get 4.

So, 4239660818 + 119900015 = 4359560833.

