Okay, we are given 405 and 6257. Let's add them up step by step.

Step 1: We'll start by adding the digits 5 & 7 in column 1 and get 12.
We'll write down the last digit 2 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 0 & 5 in column 2 and get 6.

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 0 & 6 in column 4 and get 6.

So, 405 + 6257 = 6662.

