We have numbers 2001 and 7851. Let's start adding them together.

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

Step 2: We'll start by adding the digits 0 & 5 in column 2 and get 5.

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 2 & 7 in column 4 and get 9.

So, 2001 + 7851 = 9852.

