Answer:

Step-by-step explanation:
When a charge is in an electric field, it experiences a force given by

where
q is the charge
E is the strength of the electric field
The field between two parallel plates is uniform, so it can be rewritten as

where
V is the potential difference between the plates
d is the separation between the plates
So the first equation becomes

In this problem we have:
is the magnitude of the charge
V = 250 V is the potential difference between the plates
d = 3.4 cm = 0.034 m is the separation between the plates
So the magnitude of the force is
