OK, let's do this. We've got 1540 and 4459 and we're adding them all together.

Step 1: We'll start by adding the digits 0 & 9 in column 1 and get 9.

Step 2: We'll start by adding the digits 4 & 5 in column 2 and get 9.

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 1 & 4 in column 4 and get 5.

So, 1540 + 4459 = 5999.

