Decompsotion of time domain signals into frequency component

Please provide necessary explanations leading to the answer.

a. A square wave signal with voltage levels 0 volts and 2.0 volt at a frequency of 1.00 MHz is multiplied by a sine wave at a frequency of 5.0 MHz. Which of the following frequencies are present at the output of the multiplier - there may also be other frequencies not listed below.

1.0 MHz 2.0 MHz 3.0 MHz 4.0 MHz 5.0 MHz 6.0 MHz

b. A radio transmitter operates at a carrier frequency of 99.1 MHz. The transmitter has an intermediate frequency of 10.0 MHz. A local oscillator is required in the transmitter to provide the up-conversion from 10.0 MHz to 99.1 MHz. Compute the oscillator frequency.

c. A square wave with amplitudes 0 V and 1.0 V, and a period of 1.0 ms is applied to an ideal high pass filter with a cut on frequency of 1500 Hz. Which of the following sine waves are present at the filter output, where ωo = 2000 PI radians/s: 2/PI cos (wt ) 2/PI cos (2wt) 2/3PI cos (3wt) 1/3 cos 3 (wt) 1/2PI cos 4 (wt)