A thin cylindrical shell of radius R$1=6\mathrm{.}5$cm is surrounded by a second cylindrical shell of radius R$2=8\mathrm{.}9$cm.Both cylinders are $9\mathrm{.}0$ m long and the inner one carries a total charge Q$1=-0\mathrm{.}92$ mu C

and the outer one Q$2=+1\mathrm{.}60$ mu C$.$For points far from the ends of the cylinders, determine the magnitude of the electric field at a radial distance r  from the central axis of $7\mathrm{.}4$  cm.