Finding the charges on surfaces (hollow spheres)

[rela]

Dear all,

Two hollow conducting spheres have a common center O. The dimensions of the spheres
are as shown (attached above).

A charge of −200 nC is placed on the inner conductor and a charge of +80 nC is placed on the outer conductor. The inner and outer surfaces of the spheres are respectively denoted by A, B, C, and D, as shown. In the figure above, the charges on surfaces C and D respectively, in nC, are closest to:

I got it as +80 and -120

Not sure if it's correct too as I dun have the answers.

Hope you guys will help me out in the approach of solving this questions. Having some problems in visualizing.

Thanks again for the help.

Regards
Rela

 

[pam]

The net charge on A+B+C must be zero so that E=0 in the conductor between C and D.
This means the charge on C must be +200.
Your answer for D is correct.