The call center for souq.com has five workers answering incoming phone calls for orders. If the five phone lines are busy, a potential customer gets a busy signal and this represents a lost sales opportunity. The calls occur randomly (i.e., according to a Poisson process) at a mean rate of 15 per hour. The length of a telephone conversation follows an exponential distribution with a mean of 4 minutes. What is the average waiting time on phone and the percentage of lost sales?