Consider a solid insulating sphere of radius b with nonuniform charge density [tex] \sigma = ar [/tex] where a is a constant. Find the charge Q_r contained within the radius r, when r < b. Note: The volume element dV for a spherical shell of radius r and thickness dr is equal to [tex] 4\pi r^2 [/tex]. I got this part, the answer was Q_r = [tex] \pi ar^4 [/tex]. The second part says if a = 2 x 10^-6 C/m^4 and b= 1 m, find E at r= 0.6 m. Answer in units of N/C. I used the equation [tex] E= Qr/4\pi E_0 R^3 [/tex] Plugging in the previous answer for Q gave me [tex] E= (\pi ar^4)r/ 4\pi E_0 R^3 [/tex] so [tex] \pi ar^5/4\pi E_0 B^3 [/tex] since R=B in this problem. then [tex] \pi (2 x 10^-6)(.6)^5/ 4\pi (8.85 x 10^-12) [/tex] This gave me 4378 N/C... which is wrong. Help please?