We have numbers 4221 and 4294. Let's start adding them 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 & 9 in column 2 and get 11.
We'll write down the last digit 1 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 2 & 2 in column 3 and get 5.

Step 4: We'll start by adding the digits 4 & 4 in column 4 and get 8.

So, 4221 + 4294 = 8515.

