OK, let's do this. We've got 957 and 402 and we're adding them all together.

Step 1: We'll start by adding the digits 7 & 2 in column 1 and get 9.

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

Step 3: We'll start by adding the digits 9 & 4 in column 3 and get 13.
We'll write down the last digit 3 and carry the 1 to the next column.

So, 957 + 402 = 1359.

