Answer:
14amu
Explanation:
Given subatomic particles:
 Number of protons  = 7
 Number of Neutrons  = 7
 Number of electrons  = 7
Unknown:
Atomic mass unit; amu of nitrogen
Solution:
The atomic mass unit of a substance is the number of protons and neutrons in such an atom;
   Atomic mass unit  = number of protons + number of neutrons
This is because the mass of an atom is concentrated in the nucleus;
  For the given specie;
    Atomic mass unit  = 7 + 7 = 14amu