Let's solve this addition problem. We have 8451 and 427, and we need to add them together.

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

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 4 & 4 in column 3 and get 8.

Step 4: We'll start by adding the digits 8 & 0 in column 4 and get 8.

So, 8451 + 427 = 8878.

