Let's break this down. We're going to add 991 and 63 together.

Step 1: We'll start by adding the digits 1 & 3 in column 1 and get 4.

Step 2: We'll start by adding the digits 9 & 6 in column 2 and get 15.
We'll write down the last digit 5 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 9 & 0 in column 3 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

So, 991 + 63 = 1054.

