OK, let's do this. We've got 5521 and 3404 and we're adding them all together.

Step 1: We'll start by adding the digits 1 & 4 in column 1 and get 5.

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

Step 3: We'll start by adding the digits 5 & 4 in column 3 and get 9.

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

So, 5521 + 3404 = 8925.

