Answer :
Your answer is going to be -1.
4+(-5) changes to 4-5, which equals -1.
4+(-5) changes to 4-5, which equals -1.
That's the same as starting from the lobby, taking the elevator UP four floors,
then taking another elevator DOWN 5 floors. Where do you end up ?
(positive 4) + (negative 5) = -1
then taking another elevator DOWN 5 floors. Where do you end up ?
(positive 4) + (negative 5) = -1
