15 From the time a request for data is submitted until the request is fulfilled, a database takes an average of 3 seconds to respond to a request for data. We find that the database is idle around 20% of the time. Answer the following questions, assuming that the database can be modeled as an M/M/1 system.

a What is the average service time per database query?

b What is the average number of queries in the system?

c What is the probability that 5 or more queries are present?