Answer:
The elevator stops on the 19th floor.
Step-by-step explanation:
On the 16th floor, goes up 12 floors:
16 + 12 = 28
On the 28th floor, goes down 7 floors:
28 - 7 = 21
On the 21st floor, does up 3 floors:
21 + 3 = 24
On the 24th floor, goes down 5 floors:
24 - 5 = 19
