Answer
$I=0.879W/m^2$
Work Step by Step
The intensity of light is equal to the average value of the Poynting vector, which is $$S=\frac{E_mB_m}{2\mu_o}$$ Using the relation that $E_m=cB_m$, the equation becomes $$S=\frac{cB_m^2}{2\mu_o}$$ By substituting the value of $B_m=85.8\times 10^{-9}T$, the intensity equals $$I=S=\frac{(3.00\times 10^8m/s)(85.8\times 10^{-9}T)^2}{2(4\pi \times 10^{-7}Tm)}=0.879W/m^2$$
