When using an inventory buildup diagram, 
To find λ look graphically:
λ = (30 · 6)/45 = 4
To find μ is the same, look at the capacity diagram:
μ = (5 · 36)/45 = 4 tons/hr
μ = (20 + 24 + 30)/10 = 7.4 tons/hr
Average Inventory = area of Inv Buildup Diagram = Lq
Length of time