Which phrase best describes a logical fallacy

How do you work out 21.3-8= show your working. plz

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?

Blank is the amount of energy in a sound wave per unit of time and is also related to the loudness of a sound