Let's solve this addition problem. We have 8155 and 813, and we need to add them together.

Step 1: We'll start by adding the digits 5 & 3 in column 1 and get 8.

Step 2: We'll start by adding the digits 5 & 1 in column 2 and get 6.

Step 3: We'll start by adding the digits 1 & 8 in column 3 and get 9.

Step 4: We'll start by adding the digits 8 & 0 in column 4 and get 8.

So, 8155 + 813 = 8968.

