A metal sphere with radius r_a = 1.10 cm is supported on an insulating stand at the center of a hollow, metal, spherical shell with radius r_b = 9.50...

A metal sphere with radius r_a = 1.10 cm is supported on an insulating stand at the center of a hollow, metal, spherical shell with radius r_b = 9.50 cm. Charge +q is put on the inner sphere and charge - q on the outer spherical shell. The magnitude of q is chosen to make the potential difference between the spheres 430 V, with the inner sphere at higher potential.Calculate q.