Consider 20 DS0 circuits that are multiplexed onto three outgoing circuits. The mean arrival rate at each DS0 circuit is one call per hour during the busy hour; calls last, on average, five minutes. Assume Poisson arrivals, exponentially distributed call durations, and that customers that attempt a call when all circuits are busy are blocked (ignore call retry). The probability of blocked calls is? (Use 2 digits to the right of the decimal point.)

(Hint: A DS0 circuit is essentially a traditional wired phone circuit. So, the question essentially means there are 20 incoming phone lines and 3 outgoing phone lines)