The y-component of the electric field of an electromagnetic wave traveling in the +x direction through vacuum obeys the equation ey=(375n/c)cos[kxâ(2.20ã1014rad/s)t ]. (c=3.0ã108m/s) what is the largest that the x-component of the wave can be?

Ey = 375 cos [ kx - (92.20x10^14).t ] 

the formula of the electric field of an electromagnetic wave : 
=> Ey = Emax cos (k x - ω t) 
=> Ey = Emax cos [(2π/λ) - (2π f).t ] 

then : (2π f).t = (92.20x10^14).t 
===> 2π f = 92.20x10^14 
===> f = 92.20x10^14 / 2π 
===> f = 1.46 x 10^15 hertz 

the speed of electromagnetic wave : c = 3 x10^8 m/s 

then : c = f λ 
> λ = c / f 
> λ = 3 x10^8 / 1.46 x 10^15 
> λ = 2.0547 x 10^-7 meters = 0.205 μm

You get 6 for mechanical