​ ​ A hotel has 18 floors. The hotel owner believes the number 13 is unlucky. The first 12 floors are numbered from 1 to 12. Floor 13 is numbered 14, and the remaining floors are numbered from 15 to 19. The hotel manager starts on the top floor of the apartment building. He rides the elevator two floors down. The doors open and a hotel guest gets in. They ride the elevator three floors down. The hotel guest gets off the elevator. The hotel manager rides the elevator the remaining floors down to the first floor. ​a.​Write an addition expression using negative integers to show the number of floors the hotel manager rode down in the elevator. ​ ​b. ​On what floor did the hotel guest get off the elevator? Explain. ​ ​