Okay, we are given 2100 and 2878. Let's add them up step by step.

Step 1: We'll start by adding the digits 0 & 8 in column 1 and get 8.

Step 2: We'll start by adding the digits 0 & 7 in column 2 and get 7.

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 2 & 2 in column 4 and get 4.

So, 2100 + 2878 = 4978.

