No problem, let's work through this together. We're starting with 1551 and 2123 and adding them all up.

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 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 1 & 2 in column 4 and get 3.

So, 1551 + 2123 = 3674.

