Okay, we are given 1001503991 and 5188494909. Let's add them up step by step.

Step 1: We'll start by adding the digits 1 & 9 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 9 & 0 in column 2 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 9 & 9 in column 3 and get 19.
We'll write down the last digit 9 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 3 & 4 in column 4 and get 8.

Step 5: We'll start by adding the digits 0 & 9 in column 5 and get 9.

Step 6: We'll start by adding the digits 5 & 4 in column 6 and get 9.

Step 7: We'll start by adding the digits 1 & 8 in column 7 and get 9.

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

Step 9: We'll start by adding the digits 0 & 1 in column 9 and get 1.

Step 10: We'll start by adding the digits 1 & 5 in column 10 and get 6.

So, 1001503991 + 5188494909 = 6189998900.

