question: Hint: Please answer the question requiring a floating-point number with two decimal places and provide the final value, e.g., 1.23, 1.34, 1.45, at the end.
  Question: Figure 23-42 is a section of a conducting rod of radius $R_1=1.30 \mathrm{~mm}$ and length $L=$ $11.00 \mathrm{~m}$ inside a thin-walled coaxial conducting cylindrical shell of radius $R_2=10.0 R_1$ and the (same) length $L$. The net charge on the rod is $Q_1=+3.40 \times 10^{-12} \mathrm{C}$; that on the shell is $Q_2=-2.00 Q_1$. What is the magnitude $E$ of the electric field at radial distance $r=2.00 R_2$?
  Choices:
  (A) -0.21
  (B) 0.21
  (C) 21
  (D) 0