The elevator in an office building is controlled by a program that uses negative numbers to
indicate moving down and positive numbers to indicate moving up, so the command
+7 causes the elevator to travel 7 floors up.
The elevator is at the 12th floor now. Which series of commands will bring the elevator back
to the 12th floor?
-6, -6
+3, +3
-5, -5, +5, +5
+4, +4,-4.