If machine $C$ in Step $3$ works at full capacity, what is the maximum number of steel bars waiting to be processed by machine $D$ in Step $4$ at the end of an $8-$hour day $($both machine C and D work for $8$ hours$)?$

Which of the following machines are bottlenecks, if market demand is $90$ lbs$/$hour$?$

If market demand is $90lb\frac{s}{?}$ hour, the following resource is the constraint:

By how much would the hourly system output be improved if the capacity of machine $C$ was increased to $80lb\frac{s}{?}$ hour?