9.1.1 Two dump trucks cycle between a gravel loader and a gravel unloader. Suppose that the travel times are insignificant relative to the load and unload times, which are exponentially distributed with parameters  and , respectively. Model the system as a closed queueing network. Determine the long run gravel loads moved per unit time.

Hint: Refer to the example entitled “Repairman Models” in Section 6.4.