Ready to do some math? We're starting with 7666 and 2121 and adding them up.

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

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

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

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

So, 7666 + 2121 = 9787.

