A Company That Receives Most of Its Orders by Telephone

A company that receives most 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 variable best approximated by an exponential distribution with a mean length of waiting time equal to 2.8 minutes .What is the probability that a randomly selected caller is placed on hold fewer than 7 minutes?

A) 0.0009119
B) 0.082085
C) 0.917915
D) 0.9990881