A Catalog Company That Receives the Majority of Its Orders

A catalog company that receives the majority of its orders by telephone conducted a study to determine how long customers were willing to wait on hold before ordering a product. The length of waiting time was found to be a random variable best approximated by an exponential distribution with a mean length of waiting time equal to 3 minutes (i.e. the mean number of calls answered in a minute is 1/3) . What proportion of customers having to hold more than 1.5 minutes will hang up before placing an order?

A) 0.86466
B) 0.60653
C) 0.39347
D) 0.13534