OK, let's do this. We've got 3450 and 4307 and we're adding them all together.

Step 1: We'll start by adding the digits 0 & 7 in column 1 and get 7.

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 4 & 3 in column 3 and get 7.

Step 4: We'll start by adding the digits 3 & 4 in column 4 and get 7.

So, 3450 + 4307 = 7757.

