No problem, let's work through this together. We're starting with 813 and 2013 and adding them all up.

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

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

Step 3: We'll start by adding the digits 8 & 0 in column 3 and get 8.

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

So, 813 + 2013 = 2826.

