Let's solve this addition problem. We have 3453 and 12, and we need to add them together.

Step 1: We'll start by adding the digits 3 & 2 in column 1 and get 5.

Step 2: We'll start by adding the digits 5 & 1 in column 2 and get 6.

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

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

So, 3453 + 12 = 3465.

