OK, let's do this. We've got 4389 and 100 and we're adding them all together.

Step 1: We'll start by adding the digits 9 & 0 in column 1 and get 9.

Step 2: We'll start by adding the digits 8 & 0 in column 2 and get 8.

Step 3: We'll start by adding the digits 3 & 1 in column 3 and get 4.

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

So, 4389 + 100 = 4489.

