Two concentric conducting shells a and b are of radii R and 2R. A charge +q is placed at their center. Shell b is then earthed and a is given charge q. Find the charge on outer surfaces oboth shells.

THE charge on outer surface of A will be 2q and outer surface of B will be zero because due to earthing charge  on b will flow to earth.

i have better explained it in the image uploaded alongwith.

Sorry, can''t see any uploaded image