Answer:
10000 V
0.00225988700565 m²

Explanation:
E = Electric field = 
d = Distance = 2.5 mm
Q = Charge = 80 nC
= Permittivity of free space = 
The potential difference is calculated as

The potential difference across the plates amounts to 10000 V
Area is determined by

The area of each plate measures 0.00225988700565 m²
Capacitance is determined by

The capacitance is 