We measure the performance of a telephone line (4 kHz of bandwidth). When the signal is 10 V, the noise is 5 mV. What is the Signal-to-Noise Ratio (SNR)? (Caution: SNR is a ratio of power values.)

a) 40 dB
b) 30 dB
c) 50 dB
d) 20 dB
e) 60 dB