We are presented with 546 and 21. Let's work out the sum.

Step 1: We'll start by adding the digits 6 & 1 in column 1 and get 7.

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

Step 3: We'll start by adding the digits 5 & 0 in column 3 and get 5.

So, 546 + 21 = 567.

