The average waiting time on a Thursday night for a table at a popular Chinese restaurant is $30$ minutes. If customers arrive at the rate of four per hour and both the service and arrival rates are Poisson distributed, what is the average service time?

greater than $3$ but less than $4$ per hour

greater than $5$ but less than $6$ per hour

cannot be determined from the information provided

greater than $4$ but less than $5$ per hour