We've got two numbers: 6129 and 3369. Let's find their sum.

Step 1: We'll start by adding the digits 9 & 9 in column 1 and get 18.
We'll write down the last digit 8 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 2 & 6 in column 2 and get 9.

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

Step 4: We'll start by adding the digits 6 & 3 in column 4 and get 9.

So, 6129 + 3369 = 9498.

