3- In a communication channel, the power of a signal is 75mW and the power of noise is 50W. What are the values of SNR and SNRdB? 4- Given the narrow (usable) audio bandwidth of a telephone transmission facility, a nominal SNR of 56 dB (400,000), and a certain level of distortion. (a) What is the theoretical maximum channel capacity (Kbps) of traditional telephone lines? (b) What can we say about the actual Maximum channel capacity? 5- Consider a channel with 1MHz capacity and an SNR of 63. (a) What is the upper limit to the data rate that the channel can carry? (b) The result of part (a) is the upper limit. However, as a practical matter, better error performance will be achieved at a lower data rate. Assume we choose a data rate of 2/3 as the maximum theoretical limit. How many signal levels are needed to achieve this data rate?