Okay, we are given 170 and 21. Let's add them up step by step.

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

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 & 0 in column 3 and get 1.

So, 170 + 21 = 191.

