Consider a processing system with a demand rate $($D$($t$))$ and the capacity rate $($P$($t$))$ given by the diagram below. Assume the storage room has infinite capacity and it is completely empty at time zero. The figure on the left indicates the demand over time. Therefore, from $0$ to $4$ the demand is $4500/$hour$,$ from $4$ to $8$ the demand is $1500/$hour and from $8$ to $12$ the demand is $3000/$hour$.$ The figure on the right reports the capacity of the system. Therefore, from $0$ to $8$ the capacity is $3000/$hour and from $8$ to $12$ the capacity is $1500/$hour$.$