$($b$)$ The information Table $1$ and the process diagram below describes how Irie Steel Co$.$ makes steel.

Table $1$

At two points in the steel making process, outputs from two departments are inputs to a single department. The ratio of each input is listed on the arrow that illustrates the fiow. For example, in the Basic Oxygen Fumace two $(2)$ tonnes from the blast furnace is mixed with one $(1)$ tonne of scrap handling.

$(3)$ How much can you increase the capacity of the system, by adding capacity to the bottleneck?

$(4$ Marks$)$