please help solve this question

7. [20] A second metal plate identical to the one above in problem 6 is placed a distance d below the first and a charge -Q is placed on it. In terms of the quantities given in the problem (0, 4, d), use Gauss's law, to find (a) [3] the electric field between the plates in terms of the Q and 4 (b) [3] the voltage between the plates (c) [3] the capacitance of the structure. (d) [3] the electric energy of the system