(a) We apply Gauss’s law with dielectric and solve for k :
$$ κ=\dfrac{q}{ε_0EA}=\dfrac{8..9\times10^{-7}C}{(8.85\times10^{-12}C^2/N.m^2)(1.4\times10^{-6}V/m)(100\times10^{-4}m^2)}=7.2 $$
(b) The charge induced is $$q'=q\left(1-\dfrac{1}{κ}\right)=(8.9\times10^{-7}C)\left(1-\dfrac{1}{7.2}\right)=7.7\times10^{-7}C.$$