Answer
$(B)\ 1920\frac{N}{C}$
Work Step by Step
We know that
$E_{rms}=\sqrt{\frac{I_{avg}}{c\epsilon_{\circ}}}$
We plug in the known values to obtain:
$E_{rms}=\sqrt{\frac{(0.975W/cm^2\times 10^4cm^2/m^2)}{3.00\times 10^8(8.85\times 10^{-12})}}$
$E_{rms}=1920\frac{N}{C}$
