No problem, let's work through this together. We're starting with 9021 and 815 and adding them all up.

Step 1: We'll start by adding the digits 1 & 5 in column 1 and get 6.

Step 2: We'll start by adding the digits 2 & 1 in column 2 and get 3.

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

Step 4: We'll start by adding the digits 9 & 0 in column 4 and get 9.

So, 9021 + 815 = 9836.

