Let's solve this addition problem. We have 1515 and 6364, and we need to add them together.

Step 1: We'll start by adding the digits 5 & 4 in column 1 and get 9.

Step 2: We'll start by adding the digits 1 & 6 in column 2 and get 7.

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

Step 4: We'll start by adding the digits 1 & 6 in column 4 and get 7.

So, 1515 + 6364 = 7879.

