Let's break this down. We're going to add 4645 and 2100 together.

Step 1: We'll start by adding the digits 5 & 0 in column 1 and get 5.

Step 2: We'll start by adding the digits 4 & 0 in column 2 and get 4.

Step 3: We'll start by adding the digits 6 & 1 in column 3 and get 7.

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

So, 4645 + 2100 = 6745.

