We have numbers 451 and 220. Let's start adding them together.

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

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 & 2 in column 3 and get 6.

So, 451 + 220 = 671.

