OK, let's do this. We've got 5402 and 1357 and we're adding them all together.

Step 1: We'll start by adding the digits 2 & 7 in column 1 and get 9.

Step 2: We'll start by adding the digits 0 & 5 in column 2 and get 5.

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

Step 4: We'll start by adding the digits 5 & 1 in column 4 and get 6.

So, 5402 + 1357 = 6759.

