To calculate the net requirements for Castings and Knobs, we need to consider the demand for Complete Assemblies $($X$)$ and the quantities required for each item in the Bill of Materials $($BoM$).$

Given that the demand for Complete Assemblies $($X$)$ is $137$ units, let's calculate the requirements for each component:

For Castings $($D$)$:

Each Complete Assembly requires $2$ Castings.

So$,$ total requirements for Castings $=137*2=274$ units.

For Knobs $($E$)$:

Each Complete Assembly requires $1$ Knob.

So$,$ total requirements for Knobs $=137*1=137$ units.

Now, let's subtract the current inventory levels from the total requirements to find the net requirements:

For Castings $($D$)$:

Net requirements $=$ Total requirements $-$ Current inventory

Net requirements $=274-200=74$ units.

For Knobs $($E$)$:

Net requirements $=$ Total requirements $-$ Current inventory

Net requirements $=137-149=-12$ units.

However, since we can't have a negative net requirement, we consider it as $0.$

So$,$ the correct answer is:

Castings $74$; Knobs $0.$

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