OK, let's do this. We've got 3435 and 5420 and we're adding them all together.

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

Step 2: We'll start by adding the digits 3 & 2 in column 2 and get 5.

Step 3: We'll start by adding the digits 4 & 4 in column 3 and get 8.

Step 4: We'll start by adding the digits 3 & 5 in column 4 and get 8.

So, 3435 + 5420 = 8855.

