What is the contribution margin per machine hour for couches based on the company's product mix?

(a) Define and explain the concept of contribution margin in the context of managerial accounting.
(b) Provide information on the company's product mix and its relevance to calculating the contribution margin per machine hour for couches.
(c) Explain the formula or method used to determine the contribution margin per machine hour.
(d) Discuss the significance of the contribution margin in assessing the profitability of producing couches.