(a) The height decreases by 12 feet each second towards the first floor (b) After 3 seconds, the elevator is 144 feet above the first floor After 6 seconds, the elevator is 108 feet above the first floor After 9 seconds, the elevator is 72 feet above the first floor (c) It takes 15 seconds for the elevator to get to the first floor (d) The basement floor is 48 feet below the first floor Step-by-step explanation: 31 (a) explanation: An elevator is 180 feet above the first floor. Each second, it descends 12 feet. So the elevator's change in height each second is a decrease of 12 feet towards the first floor. 31 (b) explanation: If the elevator goes down 12 feet, towards the first floor, in 1 second then; After 3 seconds it will be 180 feet - 3(12) feet = 144 feet above the first floor After 6 seconds it will be 180 feet - 6(12) feet = 108 feet above the first floor After 9 seconds it will be 180 feet - 9(12) feet = 72 feet above the first floor 31 (c) explanation: If the elevator is 180 feet above the first floor and it takes 1 second to descend 12 feet, Then it will take: × 1 second = 15 seconds reach the first floor. 31 (d) explanation: From the first floor it takes 4 seconds to reach the basement floor Therefore the basement floor is × 12 feet = 48 feet below the first floor
