We've got two numbers: 3552 and 121. Let's find their sum.

Step 1: We'll start by adding the digits 2 & 1 in column 1 and get 3.

Step 2: We'll start by adding the digits 5 & 2 in column 2 and get 7.

Step 3: We'll start by adding the digits 5 & 1 in column 3 and get 6.

Step 4: We'll start by adding the digits 3 & 0 in column 4 and get 3.

So, 3552 + 121 = 3673.

