Answer:
The wavelength of an electromagnetic wave in a vacuum is given by the equation:
wavelength = speed of light / frequency
where the speed of light in a vacuum is approximately 3.00 x 10^8 m/s.
Plugging in the given frequency, we get:
wavelength = (3.00 x 10^8 m/s) / (7.80 x 10^14 Hz)
wavelength ≈ 3.85 x 10^-7 m
Therefore, the wavelength of the electromagnetic wave is approximately 3.85 x 10^-7 meters.