Let's solve this addition problem. We have 640 and 13, and we need to add them together.

Step 1: We'll start by adding the digits 0 & 3 in column 1 and get 3.

Step 2: We'll start by adding the digits 4 & 1 in column 2 and get 5.

Step 3: We'll start by adding the digits 6 & 0 in column 3 and get 6.

So, 640 + 13 = 653.

