Let's get this math done. We have 2121 and 7704 and we're going to add them all together.

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

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

Step 3: We'll start by adding the digits 1 & 7 in column 3 and get 8.

Step 4: We'll start by adding the digits 2 & 7 in column 4 and get 9.

So, 2121 + 7704 = 9825.

