How is amplitude modulation achieved?

A) Amplitude modulation can be achieved by application of the message signal and the carrier wave to a non-linear device, followed by a band pass filter. B) Now frequency of carrier signal can be found as fc = (640 + 660) / 2 = 650 kHz. Frequency of modulated signal can be calculated as fc + fm = 660 → fm = 10 kHz. Now the band width of AM = (660 - 640) kHz = 20 kHz