Let's solve this addition problem. We have 2421 and 4222, and we need to add them together.

Step 1: We'll start by adding the digits 1 & 2 in column 1 and get 3.

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

Step 3: We'll start by adding the digits 4 & 2 in column 3 and get 6.

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

So, 2421 + 4222 = 6643.

