Given a process with two steps connected by an infinite$-$size buffer. The step before the buffer can process $80$ units per hour whereas the step after the buffer can process $40$ units per hour. The demand for processing arrives at a constant rate of $60$ units per hour starting $8$:$00$am$.$ The two steps start to work simultaneously at $8$:$00$am$.$ Which of the following statements is $/$ are valid?