A DSB$-$SC signal is given by m$($t$)$cos $(27)106,.$ The carrier frequency of this signal, $1$ MHz$,$

is to be changed to $400$ kHz$.$ The only equipment available consists of one ring modulator,

bandpass filter centered at the frequency of $400$ kHz$,$ and one sine wave generator whose

frequency can be varied from $150$ to $210$ kHz$.$ Show how you can obtain the desired signal

cm$($t$)$ cos $(27$ x $400$ x $103,)$ from m$($t$)$ cos $(2$rr$)10$t$.$ Determine the value of c$.$