Saalfrank Corporation is considering two alternatives that are code$-$named M and N$.$ Costs associated with the alternatives are listed below:

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$$Alternative MAlternative NSupplies costs$ $55,000$$ $49,000$Assembly costs$ $30,000$$ $30,000$Power costs$ $10,000$$ $15,500$Inspection costs$ $23,000$$ $12,000$

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Required:

a$.$ Which costs are relevant and which are not relevant in the choice between these two alternatives?

b$.$ What is the differential cost between the two alternatives?