Answer:
The potential difference between the plates is 8 V.
Explanation:
Given that,
Area of plates = 0.40 m²
Charge 
Distance = 4.0 cm
We need to calculate the electric field
Using for formula of electric field

Where, q = charge
A = area
Put the value into the formula


We need to calculate the potential difference between the plates
Using formula of potential difference

Where, E = electric field
d = distance
Put the value into the formula


Hence, The potential difference between the plates is 8 V.