In an opencast mine loading and transporting has been carried out by shovel dumper combination. There is only one shovel is in operation. Dumpers arrive at the rate of 10 dumpers per hour and it takes shovel on an average 5 minutes to load a dumper. Assume arrival is Poisson and service time is exponentially distributed. What is expected waiting time of the dumper in the queue?

A. $$\frac{5}{7}$$ hour

B. $$\frac{5}{12}$$ hour

C. $$\frac{12}{7}$$ hour

D. $$\frac{1}{2}$$ hour

Answer: Option B