Answer:
Option c is right
Explanation:
Given that a suburban specialty restaurant has developed a single drive-thru window. Customers order, pay, and pick up their food at the same window. Arrivals follow a Poisson distribution while service times follow an exponential distribution.
service rate per customer =

Average number of arrivals per hour = 6
Service time for 6 customers =
minutes
i.e. on an average per hour the server is buy in 45 minutes
Proportion =

Option c is right