We have numbers 1421 and 2666. Let's start adding them together.

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

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 4 & 6 in column 3 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 1 & 2 in column 4 and get 4.

So, 1421 + 2666 = 4087.

