Answer:
The magnitude of the new electric field is <u>35820 N/C</u>.
Explanation:
Given:
Original magnitude of electric field (E₀) = 2388 N/C
Original voltage = 'V' (Assume)
Original separation between the plates = 'd' (Assume)
Now, new voltage is three times original voltage. So, 
New distance is 1/5 the original distance. So, 
Now, electric field between the parallel plates originally is given as:

Let us find the new electric field based on the above formula.

Now,
. So,

Therefore, the magnitude of the new electric field is 35820 N/C.