Answer
See explanation.
Work Step by Step
a. The intensity of the light beam is $ I= (\frac{1}{2}\epsilon_0 c)E^2_{max}$.
Therefore, a graph of $I$ versus $E^2_{max}$ should be a straight line with a slope of $\frac{1}{2}\epsilon_0 c$.
b. $\frac{1}{2}\epsilon_0 c=1.33\times10^{-3}$
$$c=\frac{(2)( 1.33\times10^{-3})}{(8.854\times10^{-12}F/m)}=3.00\times10^8m/s$$
This is the expected answer.