Okay, we are given 7902 and 8010. Let's add them up step by step.

Step 1: We'll start by adding the digits 2 & 0 in column 1 and get 2.

Step 2: We'll start by adding the digits 0 & 1 in column 2 and get 1.

Step 3: We'll start by adding the digits 9 & 0 in column 3 and get 9.

Step 4: We'll start by adding the digits 7 & 8 in column 4 and get 15.
We'll write down the last digit 5 and carry the 1 to the next column.

So, 7902 + 8010 = 15912.

