Well if you want to know that you have to do this:
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Margin per chair = $80
Machine hours to produce 1 chair = 2 hours
Multiply: 80 x 2 = 160
Deluxe Chair: 160
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Margin per chair = $90
Machine hours to produce 1 chair = 4 hours
Multiply: 90 x 4 = 320
Executive Chair: 320
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Contribution Margin: $90 and $80
Add: 90 + 80 = 170
Contribution Margin: $170
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Machine Hours: 2 and 4
Add: 2 + 4 = 6
Machine Hours: 6 hours
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So, their is $170 contribution margin per 6 hours.
Hope this helps XD