We've got two numbers: 3557 and 2009. Let's find their sum.

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

Step 2: We'll start by adding the digits 5 & 0 in column 2 and get 6.

Step 3: We'll start by adding the digits 5 & 0 in column 3 and get 5.

Step 4: We'll start by adding the digits 3 & 2 in column 4 and get 5.

So, 3557 + 2009 = 5566.

