The method for working out how much they each paid is incorrect, lets look at it from a different perspective.
The 3 guys paid him $30, now he gives back $5 to the guys.
So there is $25 with the owner and $5 with the bell boy.
Now the bell boy keeps $2 and gives back $3, $1 to each of the guys.
So there is $25 with the owner, $2 with the bell boy and $3 with the guys.
Now indeed the guys paid $30 - $3 which is $27 dollars, but we can see that that is now split between the owner and the bell boy as $25 + $2 = $27 dollars.
