We've got two numbers: 2421 and 4007. Let's find their sum.

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

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 4 & 0 in column 3 and get 4.

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

So, 2421 + 4007 = 6428.

