Answer:
(A). The work done is
.
(B). The potential of the starting point with respect to the endpoint is 357.14 V.
(C). The magnitude of E is 5952.38 N/C.
Explanation:
Given that,
Charge = 4.20 nC
Distance = 6.00 cm
Kinetic energy 
The particle start from rest.
So, the initial kinetic energy i zero.
(A). We need to calculate the work by the electric force
Using formula of work done


Put the value into the formula


The work done is
.
(B). We need to calculate the potential of the starting point with respect to the endpoint
We know that.
Change in potential energy = change in kinetic energy

So, 
Using formula of potential

Put the value into the formula


The potential of the starting point with respect to the endpoint is 357.14 V.
(C). We need to calculate the magnitude of E
Using formula of work done
....(I)
Using formula of force

Put the value in the equation (I)


Put the value into the formula


The magnitude of E is 5952.38 N/C.
Hence, This is the required solution.