A spherical capacitor is formed from two concentric, spherical, conducting shells separated by vacuum. The inner sphere has radius 0.39 m and the capacitance is 108 pF. What is the radius of the outer sphere? Give your answer in meters to the third decimal place. C-->Capacitance K*C*rb-K*C*ra=ra*rb it says its a vacum so I'm using K=1 but i'm not getting a correct answer?!??!