Answer:
  E = -4000 N / C
Explanation:
The potential and electric field are related
     V = - E s
     E = - V / s
we reduce the magnitudes to the SI system
     s = 4 mm (1 m / 1000 mm) = 0.004 m
we calculate
     E = - 16 /0.004
     E = -4000 N / C