We are presented with 173 and 225. Let's work out the sum.

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 & 2 in column 2 and get 9.

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

So, 173 + 225 = 398.

