Why do protons and neutrons have the same mass, even though neutrons charge is neutral and protons and electrons charge

Question: Why do protons and neutrons have the same mass, even though neutrons charge is neutral and protons and electrons charge balance each other out?
- Keywords:
  electron,
  neutron,
  proton,
  subatomic
Asked by higgsboson to David on 11 Nov 2014.
- David Foley answered on 11 Nov 2014:
  
  Initally this was simply a definition – protons and neutrons have equal mass of 1 atomic mass unit. Presumably the reason why protons are positive and neutrons are neutral comes from the quarks that make it up. But that’s physics – beyond my understanding of science.

Question: Why do protons and neutrons have the same mass, even though neutrons charge is neutral and protons and electrons charge balance each other out?