a). What is the wavelengh of a 2.54MHz ultrasound wave travelling through aluminum?(the speed of sound in aluminum is 6420 m/s)

b). What frequency of electromagnetic wave would have the same wavelength as the ultrasound wave above?

3 answers

a) frequency x wavelength = (wave speed)
2.54*10^6 * wavelength = 6420 m/s

Solve for the wavelength

b) Use the same formula, but with 3.00*10^8 m/s (the "speed of light") for the wave speed, and the previous answer for the wavelength.
I am not getting the right answer for part b !
I don't know why though! :(
How  much  current  is  required  to  produce  a  force  of  0.96  N  on  a  75  cm  long  wire  oriented  at  right  angles  to  a  0.24  T  magnetic  field?