Answer
$Q = 27~nC$
Work Step by Step
We can use the equation for the electric field strength around a spherical shell to find the charge $Q$:
$E = \frac{kQ}{r^2}$
$Q = \frac{r^2~E}{k}$
$Q = \frac{(0.07~m)^2(50,000~N/C)}{9.0\times 10^9~N~m^2/C^2}$
$Q = 27~nC$
