The call center of a catalog mail sales company receives telephone calls according to a Poisson. process with an average of 100 calls per hour. The time required to take an order follows an exponential distribution with an average duration of 2 minutes. It is estimated that on average, when all lines are busy, each lost customer (ie, busy line) costs the company $11 in lost profits. On the other hand, the operating cost of each telephone line is $12 per hour. How many phone lines should the company use?