Let's solve this addition problem. We have 1273 and 15, and we need to add them together.

Step 1: We'll start by adding the digits 3 & 5 in column 1 and get 8.

Step 2: We'll start by adding the digits 7 & 1 in column 2 and get 8.

Step 3: We'll start by adding the digits 2 & 0 in column 3 and get 2.

Step 4: We'll start by adding the digits 1 & 0 in column 4 and get 1.

So, 1273 + 15 = 1288.

