pls tel me how to calculate the frequency of a wave of wavelength 12cm the initial power being 255, 425, 850W
the question makes no sense. is unintelligible. if you are asking about an electromagnetic wave in free space,v= c = fw ; you know w,c just solve for f.., that example has nothing to do with power.
Frequency is the measurement of the number of cycles per unit of time. You know that your wavelength is 12cm, that's the length of one cycle of your wave. You need to know how long it takes for a cycle to repeat. Convert that time to seconds and divide the result by 12 cm/cycle to get the frequency in cycles/sec (also known as Hertz).
The speed of light and other Electromagnetic waves os 300 000 000 meters per second. So, the frequency of this wave (in Hz) is 300 000 000 / 0.12 meters. That is 2500 MHz. The power levels look like they might have come from a microwave oven label, but they would not affect the frequency.