2. messages can be transmitted through a communication channel using two types of signals. the first type of signal, s, takes 1 microsecond to transmit. the second type of signal, l, takes 2 microseconds to transmit. there are three different messages that could be sent using exactly 3 microseconds: s- s - s, s- l and l - s (a) how many different messages can be sent in exactly 4 microseconds, and what are they? (b) if there are fn-2 messages that can be sent in exactly n - 2 microseconds, and fn-1 message that can be sent in exactly n 1 microseconds, then how any messages can be sent in exactly n microseconds? explain your answer