#### Answer

(a) The amplitude of the magnetic field is $8.3\times 10^{-13}~T$
The frequency of the magnetic field is $1.47~MHz$
(b) The magnitude of the magnetic field is $5.0\times 10^{-13}~T$
At x = 0 and t = 0, the magnetic field is pointing in the -z-direction.

#### Work Step by Step

(a) We can find the amplitude of the magnetic field:
$B = \frac{E}{c}$
$B = \frac{2.5\times 10^{-4}~V/m}{3.0\times 10^8~m/s}$
$B = 8.3\times 10^{-13}~T$
The amplitude of the magnetic field is $8.3\times 10^{-13}~T$
Since the frequency of the magnetic field is the same as the frequency of the electric field, the frequency of the magnetic field is $1.47~MHz$
(b) We can find the magnitude of the magnetic field:
$B = \frac{E}{c}$
$B = \frac{1.5\times 10^{-4}~V/m}{3.0\times 10^8~m/s}$
$B = 5.0\times 10^{-13}~T$
The magnitude of the magnetic field is $5.0\times 10^{-13}~T$
The direction of motion of the EM wave is determined by the cross-product $E\times B$. If the electric field points in the -y-direction, and the wave is traveling in the +x-direction, then the magnetic field must be pointing in the -z-direction. Using the right-hand rule, note that $(-y) \times (-z) = +x$