The capacitance of an air capacitor is \[15\mu F\]the separation between the parallel plates is\[6mm\]. A copper plate of \[3mm\] thickness is introduced symmetrically between the plates. The capacitance now becomes [MP PMT 1995]

• A. \[5\mu F\]
• B. \[7.5\mu F\]
• C. \[22.5\mu F\]
• D. \[30\mu F\]