12. Positive charge Q is distributed uniformly throughout an insulating sphere of radius R, centered at the origin. A particle with a positive charge Q is placed at x = 2R on the x axis. The magnitude of the electric field at x = R/2 on the x axis is: (A)\( Q/72\pi\varepsilon_0 R^2 \) (B)\( Q/8\pi\varepsilon_0 R^2 \) (C)\( 7Q/18\pi\varepsilon_0 R^2 \) (D)\( 11Q/18\pi\varepsilon_0 R^2 \) (E)\( Q/18\pi\varepsilon_0 R^2 \)