Wave from a wire antenna?

An electromagnetic wave from a wire antenna travels (from the reader) toward the plane of the paper. At time t = 0.0 s it strikes the paper at normal incidence. At point O and t = 0.0 s, the magnetic field vector has its maximum value, 3.46×10-8 T, pointing in the negative y-direction. The frequency of this wave is 2.39×106 Hz. a. What is the x-component of the associated electric field E at time t = 0.0 s? (Use the right-hand rule to determine the direction of E, and hence the sign of the x-component.) b. What is the magnitude of the Poynting vector of the wave at time t = 0.0 s? c. What is the y component of the magnetic field at point O at time 2.09×10-7 s? I already answered A and B. I just need to answer C. Please help me answer it with procedure because I dont know how to do it. Thank you!!!

Since this is a wave, the field is proportional to a sine. That is, you can write: B = Bmax sin( 2 pi f t + fi ), where BMax is the maximum value, f is the frequency and fi is the phase shift. You know that at t=0, the magnetic field is -Bmax. This allows you to calculate fi by filling in the numbers: -Bmax = Bmax sin( 2 pi f 0 + fi ) = Bmax sin( fi ). So, fi must be equal to pi. You can now get the B field at t=2.09x10^(-7) by filling everything in: B = Bmax sin( 2 pi f t + fi ) = 3.46 x 10^(-8) sin( 2 pi 2.39x10^6 2.09x10^(-7) + pi ) = -1,07x10^(-10) T At least if I typed in everything correctly.

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