Answer:
 5.704 x 10⁻² V
Step-by-step explanation:
given,
thickness of membrane, d = 8 nm = 8 x 10⁻⁹ m
Electric field strength, E = 7.13 MV/m
 = 7.13 x 10⁶ V/m
The electric potential across membrane
 V = E d
 V = 7.13 x 10⁶ x 8 x 10⁻⁹ 
 V = 57.04 x 10⁻³
 V = 5.704 x 10⁻² V
the electric potential across an membrane is equal to 5.704 x 10⁻² V