The space between the plates of a parallel plate capacitor is filled completely with a dielectric substance having dielectric constant 4 and thickness 3 mm and its capacitance is C. The distance between the plates in now increased by inserting a second sheet of thickness 5 mm and dielectric constant K. If the capacitance of the capacitor so formed is C/2 then  the value of K is

• A

  10/3

• B

  20/3

• C

  5/3

• D

  15/3