The figure shows two nonconducting spherical shells fixed in place. Shell 1 has uniform surface charge density +6.8uC/m^2 on its outer surface and radius 3.9 cm; shell 2 has uniform surface charge density +3.4 uC/m^2 on its outer surface and radius 1.6 cm; the shell centers are separated by L=11.2 cm. What is the x-component (with sign) of the net electric field at x=2.3 cm?