Let's get this math done. We have 2120 and 6660 and we're going to add them all together.

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

Step 2: We'll start by adding the digits 2 & 6 in column 2 and get 8.

Step 3: We'll start by adding the digits 1 & 6 in column 3 and get 7.

Step 4: We'll start by adding the digits 2 & 6 in column 4 and get 8.

So, 2120 + 6660 = 8780.

