Let's break this down. We're going to add 4070 and 3505 together.

Step 1: We'll start by adding the digits 0 & 5 in column 1 and get 5.

Step 2: We'll start by adding the digits 7 & 0 in column 2 and get 7.

Step 3: We'll start by adding the digits 0 & 5 in column 3 and get 5.

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

So, 4070 + 3505 = 7575.

