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?