We've got two numbers: 420 and 270. Let's find their sum.

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

Step 2: We'll start by adding the digits 2 & 7 in column 2 and get 9.

Step 3: We'll start by adding the digits 4 & 2 in column 3 and get 6.

So, 420 + 270 = 690.

