According to the Law of Conservation, 10,000 J of energy will be released and transformed into sound, heat, and mechanical energy. This is true because energy cannot be destroyed or created; it just transforms into some other type of energy.
Basically, this is saying that 80% of (x) = 2 so you have know what the whole would be. It would be 2.5 because 80% of 2.5 is 2. So because you are subtracting 7 from v to get 2.5, you have to add 2.5 to 7 to get v. V=9.5
