Answer
(a) $B_0 = 3.3\times 10^{-7}~T$
(b) $I = 13.3~W/m^2$
Work Step by Step
(a) We can find the magnetic field amplitude:
$B_0 = \frac{E_0}{c}$
$B_0 = \frac{100~V/m}{3.0\times 10^8~m/s}$
$B_0 = 3.3\times 10^{-7}~T$
(b) We can find the intensity of the wave:
$I = \frac{1}{2}~E^2~\epsilon_0~c$
$I = (\frac{1}{2})(100~V/m)^2 (8.854\times 10^{-12}~F/m)~(3.0\times 10^8~m/s)$
$I = 13.3~W/m^2$