We are presented with 8809404046 and 6820413444. Let's work out the sum.

Step 1: We'll start by adding the digits 6 & 4 in column 1 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 4 & 4 in column 2 and get 9.

Step 3: We'll start by adding the digits 0 & 4 in column 3 and get 4.

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

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

Step 6: We'll start by adding the digits 4 & 4 in column 6 and get 8.

Step 7: We'll start by adding the digits 9 & 0 in column 7 and get 9.

Step 8: We'll start by adding the digits 0 & 2 in column 8 and get 2.

Step 9: We'll start by adding the digits 8 & 8 in column 9 and get 16.
We'll write down the last digit 6 and carry the 1 to the next column.

Step 10: We'll start by adding the digits 8 & 6 in column 10 and get 15.
We'll write down the last digit 5 and carry the 1 to the next column.

So, 8809404046 + 6820413444 = 15629817490.

