As per Gauss law
[tex]\int E. dA = \frac{q}{epsilon_0}[/tex]
here
q = total charge inside the gaussian surface
now in order to find q
[tex]q = q_1 + \rho* \frac{4}{3}\pi(R^3 - a^3)[/tex]
[tex]q = -3.50 \mu C + 7.35 * 10^{-4}* \frac{4}{3}\pi(0.10^3 - 0.05^3)[/tex]
[tex]q = -2.86\mu C[/tex]
now electric field is given by
[tex]E* 4\pi *0.10^2 = \frac{-2.86 \muC}{\epsilon_0}[/tex]
[tex]E = \frac{9*10^9*2.86*10^{-6}}{0.10^2}[/tex]
[tex]E = 2.57 * 10^6 N/C[/tex]