Can someone explain what number 8 means ?

Arigid tank is divided into two equal parts by a partition. one part of the tank contains 3 kg of compressed liquid water at 400 kpa and 60°c while the other part is evacuated. the partition is now removed, and the water expands to fill the entire tank. determine the entropy change of water during this process, if the final pressure in the tank is 40 kpa. use steam tables.

How many neutrons does element x if it’s atomic number is 28 and its mass number is 87

The frequency of the fundamental of the guitar string is 320 hz. at what speed v do waves move along that string?