We've got two numbers: 3894 and 1021. Let's find their sum.

Step 1: We'll start by adding the digits 4 & 1 in column 1 and get 5.

Step 2: We'll start by adding the digits 9 & 2 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 8 & 0 in column 3 and get 9.

Step 4: We'll start by adding the digits 3 & 1 in column 4 and get 4.

So, 3894 + 1021 = 4915.

