Answer
The charge on the exterior surface of the shell is $~~-3.40\times 10^{-12}~C$
Work Step by Step
In part (e), we found that the charge on the interior surface of the shell is $-3.40\times 10^{-12}~C$
Since the shell is a conductor, there is no charge inside the shell.
The net charge on the shell is $-6.80\times 10^{-12}~C$
We can find the charge $Q$ on the exterior surface of the shell:
$-3.40\times 10^{-12}~C+Q = -6.80\times 10^{-12}~C$
$Q = -3.40\times 10^{-12}~C$
The charge on the exterior surface of the shell is $~~-3.40\times 10^{-12}~C$
