The y-value if a data point corresponding to x1

Which of the following always exist between two objects having mass ● elastic force ● contact force ●gravitational force ●magnetic force

Ahands-free device may only be used if it can be activated or deactivated with a

Case # 51173878 weighs 814 pounds; case # 51173981 weighs 803 pounds; case # 51174058 weighs 817 pounds; case 51174178 weighs 815 pounds; case # 51174248 weighs 817 pounds; case # 51174495 weighs 781 pounds; case # 51174577 weighs 828 pounds. what are the case #'s of the two cases that weigh the same amount?