Correct Option: A

The given wave is travelling in the + z direction (because of the presence of the term – 2 πz) and E is entirely in the x-direction. Now E and H direction gives the direction of travel of tower. It is concluded, therefore, that H must be in + y direction.
ix × iy = iz
Further, we know that

| H | =	|E|	and B = µ0 H
	η

η =	√	µ0	or | B | =	µ0 |E|
		ε0		√µ0/ε0

or
B = E/V

=		∵ = V	1
			√µ0∈0

or

B =	15 cos (6π × 108 t – 2πz) iy
	3 × 108

or
B = 5 × 10^-8 cos (6π × 10⁸ t – 2π z) i_y Wb/m²