Okay, we are given 73 and 4278. Let's add them up step by step.

Step 1: We'll start by adding the digits 3 & 8 in column 1 and get 11.
We'll write down the last digit 1 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 7 & 7 in column 2 and get 15.
We'll write down the last digit 5 and carry the 1 to the next column.

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

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

So, 73 + 4278 = 4351.

