Jobs arrive at a facility at an average rate of $5$ in an $8$ hour shift. The arrival of the jobs follows Poisson distribution. The average service time of a job on the facility is $40$ minutes. The service time follows exponential distribution. Idle time (in hours) at the facility per shift will be
- $\dfrac{5}{7} \\$
- $\dfrac{14}{3} \\$
- $\dfrac{7}{5} \\$
- $\dfrac{10}{3}$