OK, let's do this. We've got 7555 and 2001 and we're adding them all together.

Step 1: We'll start by adding the digits 5 & 1 in column 1 and get 6.

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 5 & 0 in column 3 and get 5.

Step 4: We'll start by adding the digits 7 & 2 in column 4 and get 9.

So, 7555 + 2001 = 9556.

