Let's break this down. We're going to add 8990 and 5577 together.

Step 1: We'll start by adding the digits 0 & 7 in column 1 and get 7.

Step 2: We'll start by adding the digits 9 & 7 in column 2 and get 16.
We'll write down the last digit 6 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 9 & 5 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 8 & 5 in column 4 and get 14.
We'll write down the last digit 4 and carry the 1 to the next column.

So, 8990 + 5577 = 14567.

