Let's get this math done. We have 252 and 391 and we're going to add them all together.

Step 1: We'll start by adding the digits 2 & 1 in column 1 and get 3.

Step 2: We'll start by adding the digits 5 & 9 in column 2 and get 14.
We'll write down the last digit 4 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 2 & 3 in column 3 and get 6.

So, 252 + 391 = 643.

